Ok I need some help. My computer shuts off by itself after maybe 60 seconds.

At first it came on something happened and a blue screen came on and computer shut off. I turned it back on but it wouldn’t go past the blue screen so I was going to reinstall the os, now the computer will come on but only stay on for maybe a minute sometimes it will start through the install portion of putting os back on and then it shuts off.

I have tried a different power supply, put different ram in, tried a different hard drive but still it shuts off after very short time.

Any suggestions on what I can do or what may be wrong. I cannot afford to pay anyone to fix it. I am thinking maybe the motherboard or processor may be bad but don’t know how to test. I cannot afford another motherboard or processor so I hope that isn’t the problem.

I could really use some advice.
Can you post what the BSOD errors are?
Are there any beeps when you start the computer?
If there are, can you count them?
Can you check that the RAM is properly seated?
Is there a lot of dust around the CPU cooling fan and heatsink?
Is the heatsink making good connection to the CPU?I built this computer myself from a barebones kit from Tiger DIRECT about a year ago. It has an Intel processor in it. When I turn it on it beeps once. I have removed the ram and tried a different one and got the same issue so I put the original one back and did make sure it was seated properly. It was very dusty inside and I have tried to clean as much dust as possible out of it. Before I blew out the dust it would come on and then I got the blue screen, after blowing out alot of the dust now it shuts off before it ever gets to that point.
I haven't tried taking the heatsink fan off and putting it back. I didn't think this would help. I don't have any sort of canned air to clean it out, I just blew inside with my mouth and used a paper towel to wipe off some of the dust. I used no liquids inside. I am just frustrated and would love to have my computer back.
If the light comes on the motherboard does that MEAN that the power supply and motherboard should be ok?Bench the motherboard [take it out of the case and set it on a non-conductive surface]. Strip the system of EVERYTHING but the motherboard / video / RAM. Boot the system. Do you POST? If so, start adding one component at a time, starting with the keyboard, mouse, etc., until the system fails. USUALLY the last component installed is the culprit...though not always.

Alan <><