Intermittant booting

[tharglet]

My PC has problems booting sometimes, as of recently. It gets past the BIOS stage, but then I just have a flashing cursor in the top-left.
I have tried removing:
All USB devices
HD IDE and floppy cables
The new PCI card I had, and sent back, as I thought it was that that was faulty
1 RAM chip at a time (I have 2x256)
(I've yet to do the other PCI cards, and can't remember removing the CDROM drives, but are these likely?)
I have also tried:
Letting the PC cool down
And it has failed to reset from Windows before (booting when hot/warm)
Changing the boot order, but it doesn't boot off the device I tell it to do first - just goes into flashing cursor syndrome.
Resetting the CMOS/BIOS (using the jumper)

So what is likely to be causing this intermittant fault, and what would you suggest doing to fix it? My HDs have been a little hot as of late, I've been leaving the case side off so they have better ventilation and conisdering buying a fan for them (If it doesn't end up in me getting a new PC!)
Thanx for any help I can get! It's an incredibly hard fault to track down as it is only intermittant (but it fails to boot more often than when it does atm)

[ShawnCplus]

hmm I had a problem like this one time it ended up being faulty ram, but the way you described it there could be a number of things, the boot order may be installing the hd incorrectly (ribbon cable backwards or on the wrong connector), the ram may not be compatible with the motherboard the bios may need to be flashed, resetting the bios may have destroyed some required settings you had originally to support the devices it could just be so many things it is indeed difficult to pinpoint the problem, you started on the right foot testing the ram but if it cant be fixed the cheapest solution I can think of is get a new motherboard, if you built that computer yourself then you know they are fairly cheap 50-70$ for a decent one. Thats all the help I can really give you without having the computer in front of me, hope I provided some help.

[tharglet]

The HD cables are the correct way round, and I didn't lose any settings (I know some computers are lousy and don't pick things up automatically without telling them, but mine detects RAM and HD changes happily)
RAM is compatible - had it for ages.
It has booted 2-3 times fine, since removing all the PCI cards. On a close inspection, it does look like the network card might have met the screwdriver once... could have caused a track or few to be dead.
I'll see how my PC boots over the next few days, someone suggested it could be the nVidia chipset on the board going funny - think they had heard of a PC dying that way.
I am leaning towards new mobo if the problem won't go away after removing everything. (that reminds me - need to plug my CD drives back in!)
Thanx for the reply