Windows 7: probably hardware related crashes - how to rule out devices

hi,
since two days my machine repeatedly crashed seemingly random - no freeze, no BSOD, - just like if it would have been switched off. i guess it might be a hardware problem.

is there any way to "test" and rule out several devices?
since i don't know what exactly is the problem i don't want to invest in the wrong parts.




here's a little more detailed description.
the machine is almost 3 years old and was running since then under almost constant heavy load.
since two days I had 4 crashes where the machine just went down without a warning... almost like swiching the power off. it did not seem to be software related since theres nothing specific i did which in my opinion could have caused the crash - i also have no idea how to reproduce it. it seems to happen randomly. out of curiosity i ran the machine for 30 minutes under full load (rendering) but nothing unusual happened.
i thought there might be a tool which constantly logs voltage (i case it's the power supply) and other things so that after a reboot it might be possible to see what exactly caused the problem. one other thing that caught my attention was, that one time i manually had to unplug the machine since it wouldn't even go to the biso screen.. i just heard the HD was doing something and the hd indicator was lit. I then unplugged all drives by hand, disconnected the powercalbe for 30 seconds and put everything back in again... then it worked. another time it also did not start up (crash occured when i was not in the room) but the powersupply fan was blowing like hell and the screen was blank too.

so my question is quite simple. how can i find out what is the cause - in case it's hardware related? (besides paying an expert; )

Welcome
Lets start with this
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7

This will show if the cause is a start up item, which it usually is.

If this does not help try safe mode, if you work in safe mode it is probably a driver

Run a full anti virus scan
Downlad and run a full scan with malwarebits; dont forget to update first.

Have a look here.. Stop 0x124 - what it means and what to try

thank you! i'll check those.