for things like cpu and ram and such, do they wear down over time? like hypothetically, if i had a 2.0ghz processor for like 5+ years, would it not run as fast as it would when it was new? and if it does, is there a way to prevent this or slow down the process of making it weaker? maybe its just my imagination but my computer has been running really slow lately. i haven't really done anything though.
ya, Your software can get corrupted over time, The digital ones and zeros get mixed up here and there. No your CPU has no moving parts so there is really nothing to wear out like that. If it develops a "leak"(short circuit) it will most likely just quit working. There is electromigration that occurs, but only at high temperatures and voltages. Read this article by Tom: http://www.tomshardware.com/2006/12/11/overclocking-guide-part-1/page2.html Good info on the subject there.
Indeed, CPUs will run as new until the day they break (most will last at least a dozen years, usually more). What will happen over time, however, is disk fragmentation. If you've installed a lot and uninstalled a lot, there will be fragments of files left everywhere on your hard disk. Running disk defragmenter regularly should help up your PC's speed significantly, as well as running an adware scan, a full antivirus scan, and editing your startup list to remove programs you don't always use (this is done by going Start->Run and typing msconfig. Look for the startup tab and untick what you don't need every time you boot your PC up)
