It doesn't make any sense to just guess and start replacing parts that you aren't sure are bad. I'd start with running check disk. Open a command prompt: Click Start>>Run and type CMD in the box & hit enter. type CHKDSK /R
at the prompt and hit enter. A message will display asking if you want to run check disk next time your computer restarts - type Y
and restart the computer.
If you think you've had a problem with dust build up before, you could try cleaning inside the case and then reseat your memory. I would use compressed air made for cleaning electronics.
To remove and reseat your RAM, power off the computer and leave it plugged in. Touch a bare metal part of the case to discharge any static build up. Remove each stick and replace it, making sure you hear the locking tabs click. Handle the RAM at the top corners making sure you don't touch the memory chips on the side.
There are a few other easy tests you can check as well. Go into BIOS and write down your voltage readings then post them here. If you can burn an ISO image file to CD, download a copy of Memtest86+
and boot to the disc to run a memory test.