Re: cleaning up my computer
Assuming that the PC hardware is likely to be much the same as it was back when it worked efficiently, you are left with only a few things which make it slow down noticeably.
1) All of the extra data/software which is always coming down your pipeline.
As your hard drive fills, gradually up with all of that stuff, it gets slower and slower.
Tregonsee mentioned programs which start up and run in the background. You can look in CCleaner (in the start up section) to see what there is. It is OK to disable everything in there to see if performance improves. You may have to re-enable some if you lose some required app - Laptops are often prone to have their drivers installed that way!
2) Running CCleaner will help get rid of heaps of software fluff. Just run CCleaner on the basic delivery settings.
(Fluff, to me, is the data put there, and left there, by S/W updates, antivirus updates, etc)
3) Defragging has just about disappeared over the horizon. If you have a Hard Drive larger the 500 Gb, I wouldn't bother. It was true that there could be lots of breaks in writing to the disk which would result in the drive having to lose time to find your stuff and put it together, but it would only be a problem if you had a smaller HD.
3) Your Software gets bigger every time it gets updated. Are there apps on there which you never use?
4) If you are into photography and videos - these are big space grabbers. They are better kept in a separate partition, on your hard drive.
5) I won't even mention GAMES!
Hope this helps. Remember to tell us make model of machine - how much memory, what size hard drive.