GA 790FXTA-UD5 won't boot, no beeps, constant reset?

[thx1138]

I have the following system and it isn't starting. Here are clues I have collected.

• The case power light appears to flicker in a way that suggests to me that it's maybe switching on and off constantly.
• Pressing and holding the power button does not turn it off.
• There are no beeps.
• The monitor stays in stand by.
• Removing one graphics card and three of the four memory modules does not permit booting.
• The CPU and case fans turn on apart from one which appears to have seized.

OS: Win 7 64-bit
Mainboard: Gigabyte GA 790FXTA-UD5
CPU: AMD Phenom II 965 X4
RAM: OCZ Black Ed 2x2GB DDR3-1600 + Corsair 2x2GB DDR3-1600
Graphics: 2 x Crossfired Sapphire HD 5770 1GB GDDR5

Does anyone have an idea of what to do next? Thanks.

[autotech]

Remove the power cord then remove the batter on motherboard for 5 minutes then put it back together does it help. Constant rebooting is usually faulty CPU or bent pins it is the first thing that bios checks.

[Tiger]

By mixing memory kits together, there may be compatibility issues such as unable to boot or unable to operate at rated specifications.

[autotech]

Glad you caught that tiger I missed that he mixed memory.

[thx1138]

Glad you caught that tiger I missed that he mixed memory.

It's really nothing to do with the memory. The PC booted just fine for a few months before this occurrence and removing the newer modules does not permit booting.

I have further information and developments.

The fault was likely the PSU. I measured voltages from the PSU and they were out of specification: 12 V was 10.3 V and 5 V was 3.5 V. I replaced the PSU (with XFX TS 750 W) but this has not permitted boot either. I connected a speaker to the header on the motherboard and I get a single beep. I would say it sounds like a long beep but I can't say for sure. After several seconds the beep reoccurs (here is an audio recording). I'm not sure that this qualifies as continuous long beeps - I think it might be the motherboard continually resetting. The CPU bins cannot be bent since it hasn't left its socket in five years. Is it likely to have been damaged by the low voltage?

Clearing the CMOS does not help, in case you wondered.

Edit: Never mind. The new PSU fixed the issue. One of the RAM DIMMs wasn't inserted fully which is why it wouldn't start after putting in the new PSU.