Crashing Due To Ram Problems

[canadianicon2]

setup:
vista ultimate 64bit service pack 1
intel D945GTP mobo ( latest bios installed )
pentium d 3.0GHz
100GB WD SATA HDD
Geforce 7600GT (latest driver installed )
Hercules Muse LT sound card ( latest driver installed )
Samsung DVD drive
Some generic CDRW drive
2x120mm fans
Sparkle power supply 400W

2 x 1GB patriot ( PSD21G8002H) w/blue heatspreader PC2-6400 5-4-4-14
2 X 1GB OCZ platinum (OCZ2P800R22GK) w/heatspreader PC2-6400 4-4-4-15

*could have the last timings reversed *

problem:

upredictable system hang or unassisted restart when all 4 sticks installed
stable system when only 2GB installed ( same brand or mix-n-match)
stable system so-far when only 3GB installed (asynch mode, would like to avoid)
no matter what the setup is bios reads memory okay
when all 4 installed auto setting in bios sets last timing value to 13. have manually changed this to 15.
manually changed timings to 5-5-5-15 to run all memory slower; no solution

mobo req's 1.8V ram. patriot is 1.8V and OCZ is 1.9V. HOWEVER, when only both DIMM's of OCZ installed the system runs fine.

Please suggest anything. Hopefully all info is there. Let me know if you need anything else.

[Monty007]

Try and run memory diagnostics tool in Vista, go to>vista orb>type in memory >and run a full scan.