What is "BIOS STD" vs "BIOS ALL"?
This is the stand-alone MEMTEST program from here, right?
http://www.memtest.org/
I never recalled it had such options.
Just wanted to make sure you're NOT JUST running the BIOS BUILT IN
memtest which never will be enough of a test to give you total confidence
everything is working right, though it's OK for a quick check (obviously it SHOULDN'T
have errors).
Anyway I'd personally note down all your BIOS settings so you know
what to restore them to if needed, then physically turn off and UNPLUG the PC,
boot into BIOS, "Reset all settings to BIOS defaults", save that and exit,
pop back into BIOS and change all settings so your CPU / MEMORY / Motherboard
runs at 100% stock speed and stock voltage, nothing overclocked.
Run memtest86+ from CD and see if that works.
If not, try "Reset all BIOS settings to fail-safe defaults".
Test again.
If you still have problems, turn off the PC, use a blower to blow out all
the dust you can from the top/sides/bottom of the motherboard, the CPU,
the PSU, everything.
Physically remove the DIMMs, blow dust off the DIMMs and sockets,
look for cracks/corrosion/whatever, and reseat them carefully locking them in.
Reseating your CPU might eventually be called for but I'd do that as a last resort.
Check your PSU voltages with the BIOS built in hardware monitor and verify
that none of your 3.3, 5, 12 voltages are more than 5% too low or too high, ideally
within 2% or 3%.
Try with a new power supply of appropriate size to see if that helps.
If it's still not working with memtest, there's probably a hardware problem
and you should try to track it down to PSU, CPU, memory, motherboard, so you
can replace the defective thing.