Testing the hard drive and the RAM modules is as good a place as any to start troubleshooting symptoms of that nature.
Hard drive testing: If the hard drive is less than 3 TB capacity you can test it with
Drive Fitness Test for DOS. Download the CD image from here:
http://www.hgst.com/support/downloads/legacy-downloads#DFT
Install ImgBurn & use it to create a CD from the CD image:
http://filehippo.com/download_imgburn
Boot your computer from that CD, choose "ATA only" from the menu, then press <Enter> to continue loading the testing utility.
RAM testing: Download the CD image (ISO format) from here:
http://www.memtest86.com/download.htm#free
Create the CD with
ImgBurn and boot your computer from it. Test each RAM module separately (by removing all but one) so you know which one (if any) is faulty.
Memtest should find any RAM errors usually in the first five passes of each module test so there's no need to run it beyond that if no errors are reported.