MB: Asus P5K-VM
Memory: Name brand 4x1GB sticks
cpu: E8400, E7500

PC has been working fine for years, then for the last 2 weeks it's been randomly freezing and rebooting in WIn8. Bios frequently hanging on Sata detection. PC will run for hours with Prime95 or IADA64 stability and even Intel burn in. The crashes are during general use. It does however fail stability tests with the ddr2 400 at rated speed. I have to underclock it to 667mhz to consistently pass the tests. I tried with 1, 2 and 3 ram sticks, changed sata cables, clr'd cmos, swapped cpu's and HDD's, reinstalled win8 and a new PSU but it would always freeze or reboot eventually. Cpu temps ~ 30C

Today, it finally would not boot at all, no beeps, no display, just the cpu fan would run for 3-4 secs and stop, then repeat. Removed every device and all memory with the same result. Removed mobo and checked for any grounding. Removed the cpu and inspected and cleaned the pins (compressed air) . Finally got a beep and bios display with one stick of ram, then added devices and ram back one at a time. It worked until I populated slot #1 (tried 2 diff sticks) at which point I got no bios screen. Removed slot1 ram and all ok again.
Slot 2,3,4 are all populated.

So, it appears there are 2 problems:

1. The cpu socket dirty or not making consistent contact. (hopefully fixed for now)
2. Memory slot 1

Am I overlooking anything?