In my many years of dealing with blue screens, I frequently find that a flaky power supply can also cause an intermittent BSOD. Typically one of the rail voltages sags, or collapses momentarily under a heavy load, enough to cause a RAM or disk read/write error and a resulting BSOD. Try placing a known good PS next to the sick PC and disconnect the existing PS cables, but don't physically remove it just yet. Connect the known good power supply cables and then run a RAM test, or better yet a burn-in test to stress it. I like to use: Stability Tester, Burn-In Tester, or Passmark CPU Burn-In, for stressing power supplies. Anything that will heat up the CPU and motherboard chips. If the PC no longer experiences a BSOD, then replace the weak power supply.

Make sure the new power supply has a high enough power (Watt) rating to support all of the current devices installed. Also stay away from moderate size power supplies with multiple rails. Single rail power supplies work the best in the 400-650 Watt range suitable for most desktop PC's.

You see this problem frequently on under-powered big name desktops, where the owner has added a high-end gaming graphics card with no regard to the power supply rating. Frequently these big name brand units ship with small 300-400 Watt power supplies from the factory. Adding more RAM or a graphics card can push these weak power supplies past their limits.

I have also seen flaky hard drives cause a BSOD. A failing hard drive will produce a read/write error or suddenly go offline, due to bad sectors or head errors that will give a distinctive BSOD error code. I forget the code number off the top of my head, but you can Google it like the article says and it will tell you to run a disk check on the hard drive.

I have also seen memory errors caused by noisy power supplies that produce too much ripple in the DC output. You can view this on an Oscilloscope, or just try another power supply. As power supplies age the Electrolytic filter capacitors start to dry out and loose their capacitance. This causes the AC ripple to increase, especially under a heavy load. Avoid low-cost power supplies as this is one of the areas they like to scrimp on. Look for power supplies with a 5-year lifetime warranty.

I typically use a 450 Watt Bronze PS in my basic desktop builds. If it's a gaming rig, then I scale upwards according to the number and type of graphics cards the buyer wants installed. I typically go with a 650-750 Watt PS with a single high-end gaming graphics card and dual hard drives. With dual graphics cards I usually install an 800+ Watt PS.