Boot up – Lock ups

When I power up system,it will lock up after it checks NVRAM, other times it locks ups after SMART drive check, and then other times when it searches for IDE for RAID configuration and then sometimes I could just click on an item or performing a task and it will lock up and then go blank and then monitor power turns amber instead of green.

Power supply and fans are all working-temp is cpu is 40 celsius and MB is 42.

Video card and memory seem to be in tight. I have an AMD 3700 proce with 1.5 gig ram- 3 slots full, nvidia video agp card, antec power supply 450.

I cannot isolate the problem- is it video or ram???

Thanks

bob