I've been experiencing many issues lately that nothing has solved. It mainly consists of randomly freezing and restarting with no error screens. It typically happens when i'm trying to boot into an OS or run a program.
The restarting/freezing occurs in safe mode too, but not when running commands such as chkdsk. I swapped PSU, GPU, HDD, and reseated everything else. A live boot of Ubuntu via usb also freezes/restarts.
I ran Windows Memory Diagnostics and it finished with no errors. Then I ran Memtest86 v4.20 off of the Ubuntu usb and it has frozen 3 times, all on test #5.
Since the patterns are random, it has frozen at 7%, 11%, and 70%. It has no errors up to this test. The test is still moving (underscore and + are flashing) but doesn't respond to input.
Once I force a restart, Ubuntu no longer runs. Instead it says "SYSLINUX 4.04 EDD 2011-04-18 Copyright (C) 1994-2011 H. Peter Anvin et al" At this point I have to install it on the USB again in order to run another test.
The reason why i'm debating RAM vs Motherboard is because the windows diagnostics passed and I have symptoms of a faulty motherboard, but the consistent test #5 failure is interesting. All computer temps are normal.
Athlon II x3 455 3.3ghz CPU
Antec Basiq 550w PSU/Logisys 480W PSU
PNY 4gb(1x4gb) 1333mhz RAM
Radeon HD 7750 GPU/GTX 660 2gb GPU
Western Digital 250gb HDD/Hitachi 250gb HDD
Asrock 970 Extreme3 Motherboard
check your cpu temps..make sure the thermal paste has not dried out. on older rigs i seen failing power supply that have to much ripple or the voltages are bouncing cause lock ups.see if someone has a volt meter see if running memtest the system voltages stay within atx spec or use hardware monitor to see if there holding. with ram start with one dimm put it in one slot and run memtest. if it fine add 2x dimm and move the known good dim into another slot. rule out failing ram or a bad ram slot.