Computer's starting to go out.

Last night I changed a setting on Firefox and shut down my computer, and when I booted it up in the morning, Firefox took forever to open, and when it did it would freeze. Finally got it to open properly, and I changed my settings back, and then it did a similar thing with another program. For some reason Renoise has been unaffected by this. Looks like I’m gonna need to back up my info and get ready to look for a new one.

Any advice as to what might have caused this?

Overheating? try cleaning your computer fans and coolers of dust (which collects heat easily).