Compressed files corrupted for no reason

I've noticed a number of compressed files which I download are getting corrupted after a few days. When I first downloaded them, they work fine but later on when I return to unzip them, they show up as corrupted. This is also happening when I'm installing large programs. What is going on? Is my hard drive failing? Windows is still working and Scandisk is not reporting any errors.

Your hard drive sounds like it's fucked. Try booting to something like Knoppix, just to make sure it's not an operating system problem. You might try putting it in another computer and using it to see if it's a hardware problem. If it is the hard drive, stop using it. You might be able to recover some things by mounting it read-only or by sending it to a data recovery place.