When I pressed the on button, it started for a second and then stopped. It then repeated this process every 4 or 5 seconds without me touching the on button again.
before the problem I was have
Intel core 2 duo E5700
Motherbord : G41m sp20 ms-7592
I replaced the cpu by Pentium 4 to try a overclock , but I was stupid because I didn't use a Cooling paste ... the temperature was 95 in bios so I switch of the power quicky then I removed the Pentium 4 and replaced it by E5700 ...
I tried to switch on the power and problem starts...

Given the age, working on this old gear can break it. The shop if it sees this will advise the client find a working machine and salvage what's good in said machine.

95C won't kill those Intel CPUs so that's not it. But age and stress from the work can break solder connections so you know to work lightly and refuse machines this old at the service counter.

-> Find another working PC to salvage what you can. Most likely a motherboard failure.

"P35 chipset mobos start for a few seconds, turn off for a few seconds and restart on initial boot. BIOS plays a role in this behavior.
Try resetting CMOS. A BIOS update would probably help, but appears you probably can't boot from a floppy to flash BIOS."
This is suggested solution from someone, I didn't try it yet but I think that motherboard is broken :/ , I don't want to buy new one if it's necessery because my pc is weak starting from power supply 200 w.... in this point I should buy all thinks from zero :/
@rproffitt

While PC details are slim, 200 Watt power supplies and the age of the PC are working against you. If the client would pay for the tech time we would try another PSU on the tech bench. But the issue of age is front and center. We know to never work on old working PCs of that or older times unless it's something simple like a new drive or such.
-> Try again but unplug HDD, etc to lighten the load. Even then the cost of a new power supply will fetch a Core2Duo desktop from Ebay here.

The motherboard is working very well know... It was from overclock .
Now I want the update of this bios
msi g41m-sp20 ms-7592 ver 7.1 bios
My version is v32.2
The official site of msi does not showing it so :
what I must do now ?!

What is "working well know"? "know?"

About the BIOS, the question on the BIOS is put to the motherboard maker. ALWAYS. Why? Because no one should tell you how but the maker. Or tell you to have a shop do this.

But if I take it all is working, we don't update the BIOS.

It's ok,
"Know" ?! : it's a mistake I don't know how I did it, Probably the fault of keyboard (Android : Auto Correction).

Anyway thanks you,

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