[Cal3030]

Hi! I have a 2 year old HP Pavilion P615y.
It has AMD Athlon x2 7550
8GB Memory, 750GB Hard Drive
Motherboard M2N78-LA (Violet)
NVIDIA GeForce 9100 integrated graphics
Windows Vista Home

After pressing power on button, power on light stays on, HDD light on solid, power supply led on solid(in rear of case), display blank.
The CPU and case fan start and then shut down after a few seconds. I've disconnect everything from the motherboard (HDD, DVD drive and RAM) with same results, also install all RAM modules individually, tried resetting CMOS by removing battery and setting jumper, the power supply is putting out 3.3, 5 and 12 volts.

[phillpower2]

Hi Cal3030
Possible causes include a bad PSU, overheating or a system short.

Quote

the power supply is putting out 3.3, 5 and 12 volts.

How did you establish this?
See Digeratis canned text regarding testing PSUs @ http://www.geekstogo...-a-psu-problem/

[Cal3030]

I Check the voltage at the MOB/PwrSup connector with DMM.

[phillpower2]

Quote

Digerati states To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

When the computer is doing nothing more than sitting at the desktop the PSU is not being stressed in any way, start multi tasking, gaming or using demanding 3D software and a flaky PSU will become even more unstable.
Trying a known good PSU is a priority, especially if you have the stock HP type as brand names tend to use minimum power and quality units to keep costs down, what is the brand and output of your PSU?