Think you might have a bad RAM module in your PC? Freeware utility MemTest86+ will run a memory diagnostic to help you find out. Before I explain more, a true story...
A few days ago my laptop froze up in a scary way: the screen turned into a mosaic of lines, boxes, and other visual oddities. I powered down, rebooted, and got back to work - only to encounter the same lockup about 20 minutes later. Uh-oh.
This wasn't some Windows glitch or malware infection, which would have resulted in the usual error messages or flaky system behaviour. No, this was almost certainly a hardware problem. The laptop in question was a couple years old, and it had banged around a fair bit inside my backpack. Maybe the screen was starting to go?
Then I remembered that just a couple weeks earlier, I'd installed a new RAM module, raising the total system memory from 2GB to 4GB. Aha, I thought, that has to be it: bad RAM.
My first troubleshooting step was to remove the new module, then run the system and see if it locked up again. It didn't. That's when I decided to bring in MemTest86+, to help me determine if the new module was indeed faulty.
In the old days, running MemTest86+ meant burning it to a blank CD and booting the system from it - a huge hassle any way you slice it, and a potentially ineffective solution for laptops that lack optical drives.
Fortunately, there's now a flash-drive version that's a snap to install and use. Just find any old drive (size doesn't matter; the utility is all of 125K), then download and run the "Auto-installer for USB Key." Do note that this will require wiping the drive, so make sure you don't have anything important on it.
Then just reboot your PC with the flash drive inserted. (You may need to hit the BIOS or load a boot menu at startup to make sure the system boots from the drive.) MemTest86+ will start testing immediately, and report any errors it finds. (The entire suite of tests can take a while to complete.)
MemTest isn't the most user-friendly utility on the planet (a lot of the data and commands are Greek to me), but ultimately it can answer the question of whether or not you have bad RAM. If you do, it's a very likely explanation for frequent Blue Screens of Death and other system glitches.
Interestingly, MemTest found no errors in my RAM. And ever since reinstalling the new RAM module, the system hasn't crashed again. So I now think that the module wasn't properly seated the first time, or perhaps got nudged loose by all my jostling. Time will tell.