how can I tell if I have bad RAM?

It's probably not seated right. Power supply problems could do it too. Should fail on powerup. Put it in a friends machine and test. Sometimes adding too many marginally built sticks can cause problems (Syncmax memory has trouble when adding 4 sticks to many motherboards, draws too much power off the memory addressing chips on the motherboard)

i had a bad stick once and my computer beeped like six times when i turned it on, and it wouldn't load at all.

yes, make sure it's seated properly I tip the case very carefully so the motherboard is flat to the ground. It easier to get that sucker in there and there is better light Then make sure you discharge any static you might have by touching a metal piece of your case. If you have RAM already installed I suggest you remove it to test the new RAM. for Dimm memory. Make sure the notches line up then push that sucker down firmly. then turn the case back try booting if you get beeps try reseating it again. if you can't get it to work or it doesn't boot try returning it. If you got your RAM locally chances are they will swap it. always get RAM with a lifetime warrenty. If you want tools try http://www.eurosoft-usa.com TheGorx Windows Help

Oh...my question was more along the lines of, the RAM I installed months ago, and windows etc. loads up fine, but lately, even after a fresh reformatting like a week ago, my computer seems to be lagging. I was wondering if there was something wrong with the RAM?

You might check you bios for optional settings. But I'd check in windows system monitor to see how much free Ram you have at any given time. Basically if the RAM boots Windows when it's the only stick in there and the system or windows doesn't report anything. or rebooting and registry error don't occur. I'd say it's fine. But there are Dos utilities and windows utilities that can scan your memory.

by the way you might want to add or repost with more info such as system /motherboard the RAM you upgraded and total amount. I'm not a real big memory expert I've been pretty lucky I guess no big problems to gain experience from. But I do know a few tweaks for windows if you find that windows is hogging all the RAM that was just added.