You shouldn't need to format. My system is fine and once in a while any Windows app will crash. Your RAM handles everything you are doing, every program, every game, the operating system... so if it is corrupt you can get reboots, system crashes, application crashes, erroneous error messages etc... If it crashed while a file was being written you might get some corrupt data (like a corrupt save game or word document), but there should be no permanent damage.

You have already replaced your hard drive, so even if there was a problem with it there likely is not now. If you want to or for in the future, there is a nice little hard drive fitness test from Hitachi that I like to use, located here:

http://www.hitachigst.com/hdd/support/download.htm#DFT

Download the CD image ISO, and burn it to a disc. You also boot off of the CD, this one has some options, just hit enter until you get to the screen where you select the desired hard drive from. You may get an error message or two about being unable to find certain things...that is fine. You will see a list of your drives (Hard drives, cd drives etc...). Just choose your hard drive and choose quick test. This should only take a few minutes. If it passes go ahead and do an advanced test, but be warned this can take a few hours or so. If it fails, a large red box will appear saying an error has been found on the non-Hitachi drive (unless it is actually a Hitachi drive). That means there is something wrong with the hard drive.

But you shouldn't need to do this since we have found the RAM is bad, and you mentioned that you have replaced the hard drive already.