Vista 64 install issues

System:
MSI p35 Platium Combo
Intel e8400
4gbs corsair ddr2 667
Leadtek 9800gx2\
Gigabyte 800w Odin
Antec p182, 3 x 120mm fans
Pioneer 20x dvd burner
OS:
WD Raptor 74gb
Vista Ultimate 64
(no new hardware recently installed)

Issue:
Random freezes gaming and surfing and idle. A reboot fixed these (happened maybe 10-15 times in a month) Froze for good after installing some bad software. Rebooted to find that I couldn't get passed the black screen w/ green bar.

Fixes attempted:
1. Format / reinstall
install successful, vista rebooted itself after about 1 minute, cant get pass black vista loading screen again/

2. Memtest+
Failed, some tests, isolated to one stick of ram, removed. Now using 1x 1gb stick that passed the test.

3. Restored defaults to bios, bios already at latest version
no difference

4. Ran windows memory test on remaing 1gb stick
Passed

5. Ran WD Data Lifeguard tools
Updated MBR, formated using this tool.

6.Reinstalled Vista (different version)
No difference

7.Reinstalled vista (same version)
No difference.

8. Unplugged all other hdd's

9. Ran Viguard hdd diagnostic, passed.

10. Ran CPU stress test, passed.

11. Raptor hdd seems to be running quite hot, ran SEAtools dos, Passed short test but gave temp warning.

Please help, im totally stuck!!!

4 x 1 or 2 x 2?

Make sure the RAM is set to mfg spec voltage in the BIOS.

If you are using 4 sticks of RAM you may be having an issue we see with many motherboards - when all 4 slots are filled you may need to tweak the speed/timings to a more conservative level and possibly set RAM voltages a tick or so higher than spec. to get it stable.

More info and exact RAM model number and we can be of more help.