Computer will only POST sometimes.. and won't detect HDD when it does

[Vestral]

I was playing a game on my (~2 yr old) computer a while ago when it locked up on me, and then crashed. Since then, when attempting to power on the system, one of 3 things will happen:

1) It will successfully POST, and then give me an "DISK BOOT FAILURE, INSERT SYSTEM DISK AND PRESS ENTER" message.

2) It will successfully POST, and then I will boot from the dvd drive. However, the hard drive will not be detected.

3) It will power up, but the fans will remain at full power (instead of slowing down after a moment) and nothing will be sent to the monitor.

If I leave the system off for a while and try to power it on, I will consistently be able to get scenario 1 or 2 above. Once I get one of these scenarios I can leave it running seemingly for as long as I like (for example, while running memtest for hours, no problems). However, I can only get it to POST once or twice before I start getting the 3rd scenario above and have to let it sit for a while again.

An additional odd symptom: when powering the system down with the normal power button on the case, it sometimes turns itself back on shortly after (unless I flip the PSU switch of course).

Things I have tried that have not altered the symptoms:
-Running one stick of RAM or the other instead of both (also ran memtest, no errors)
-Disconnecting HDD and DVD drive from mobo/PSU, leaving only mobo, RAM, video card, PSU, CPU/heatsink inside the case, and keyboard, monitor, power cord attached outside the case.
-Replaced motherboard
-Replaced PSU
-Plugged computer in at a different outlet that powers other computers without issues

Any help/suggestions are greatly appreciated as this is driving me crazy trying to fix this.

Computer specs:
CPU: Intel Core2 Quad Q9450
Mobo: GA-P43-ES3G
RAM: 2x 2-gigs DDR2 800 MHz
PSU: Antec BP550 Plus (550W Continuous power)
Graphics Card: Nvidia Geforce 9800GX2

[Techi]

is it an Antec case? does it have a tiny little switch at the back of the tower?

a while ago i had to do telephone support to deal with similar bizarre symptoms without solution for weeks. in the end the user shipped the unit to me. i discovered that there was a tiny little switch at the bak of the tower that was to control CMOS set/reset. the user accidentally left it in the wrong position hence the mysterious problems. if i had never physically seen the case, i would never have guessed there was such a little switch. his PC has been fine ever since.

also there might be some red LED light HEX code on MOBO (tho the lid has to be off to see the code). if u get a number usually it means something. u should be able to decode and find out what the problem is.

[Vestral]

It is an Antec case (Antec 900) but I don't see a switch at the back of the case. The CMOS settings don't seem to be getting reset either. Also, the motherboard seems to have no LEDs. My previous mobo did have some LEDs but I believe they were related to energy star power consumption.

[Techi]

Do u mean you are unable to reset CMOS? Is the CMOS battery gone? I don't know whether Antec 900 has an external CMOS slider switch (similar to its fan switch) but the one I saw was so tiny that most users would never have noticed its existence (near the I/O panel).

The error code (LED) would be very useful to interpret what the problem is. It changes during bootup to let u know what's going on.

Can you hear any bleeps during POST?

1 short: System boots successfully
2 short: CMOS setting error
1 long, 1 short: Memory or motherboard error
1 long, 2 short: Monitor or graphics card error
1 long, 3 short: Keyboard error
1 long, 9 short: BIOS ROM error
Continuous long beeps: Graphics card not inserted properly
Continuous short beeps: Power error

Here's the motherboard manual from gigabyte (the manufacturer of this MOBO)
http://download.gigabyte.eu/FileList/Manual/motherboard_manual_ga-p43-es3g_e.pdf

[Vestral]

Sorry I meant that the CMOS settings aren't being automatically reset against my wishes. I can reset them manually if I want to. Unfortunately, I don't have any case/motherboard speaker so there is no beep code. As for the motherboard LEDs, I don't see any at all (with the side of the case off of course) whether it boots beyond POST or not. I will go out and get a speaker for the motherboard probably tomorrow. I appreciate the suggestions btw Techi.

I'll elaborate a little on the symptoms in case it sparks any ideas from anyone. When I turn on the machine after it's been off for a while, it starts up fine, gets through POST and then gives me the disk error. If I either leave it on for a while, or if I try to turn it on/off a few times, it stops turning on and gives me the blank screen + fans going full power and not slowing down. This is also when the power button stops easily turning off the computer, requiring that I hold it down, or switch it off at the PSU switch. If I hold down the power button, the system turns off, and then maybe turns itself back on once I let the power button go, or sometimes it just stays off.

[Techi]

1. For the time being, u could use a headphone instead of a pair of speakers. Listen to the bleeps. What is the sequence?

2. You are able to reset CMOS, where/ how would u do that?

3. What is the current MOBO (same model as before)?

4. Is the screen POST error message always about Disk Error?

5. Were u online at the time when it first crashed playing game? (just checking to see if hard drive is infected. if BIOS not protected, could also happen).

6. Have you tried a different hard drive? (elimination strategy)

That Antec user I mentioned described the symptoms very similar to yours. (Only difference was his POST message: "CHECKSUM ERROR - DEFAULT CODES Press F1 to continue or Del to enter Setup". This all started when his PC was infected with the bogus AntiVirus2010 then just one thing led to another. It drove him crazy for over a month when no-one else could fix it (how could they if they didn't know the Antec and a-Bit designs which are supposed to be "superior" but unfortunately also means things are more complicated). He eventually shipped it for me to fix when he'd run out of options.

When I got his Antec (SonataII), first thing I did was find the Hex error code then deciphered it. Once sorted the CMOS issue (I changed a new battery too just in case), I updated the BIOS. Finally protected the BIOS so it wouldn't get infected again. It's been over a year still running well (installed a good firewall etc).

[jeffreylee]

there would be following issues..
1-because of CMOS setting not set correctly.
2-hard disk power connector loose or data cable.
3-dead mother board battery
4-hard disk hardware problems