Did I delete something I shouldn't have?

[Quiet Stranger]

Okay so recently I went about deleting things off my computer that I wasn't using anymore and things (I thought) I wouldn't need. Now before that games ran just fine, L4D, TF 2 and anything else I can think of. Since the deletions my FPS in L4D 2 (so now I know the lag in all my games is an FPS problem) went from a regular 20 to 30 down to single digits. Is there some file or program on computers that makes sure games run properly? Again, EVERYTHING worked fine until I started deleting things from my computer, now it seems the only game that doesn't lag out on my is Lone Survivor and that's probably because it's such a low maintenance game. What could I have done wrong?

 

[Erana]

First off, tell us more about what you know you deleted, might have deleted, or at the very least, the method you were using to decide what files you didn't need.
Be as encompassing as possible. With this little detail, I don't really think anyone can help you.

Also, it would be helpful to know things like what OS you're using, your computer specs or some general hardware information if you've made any hardware upgrades, and the likes.

Also, has your computer recieved any sort of bump or drop of some sort? Is any other aspect of your computing experience affected?

 

[Smooth Operator]

Well either try running a recovery or start reinstalling drivers, directX, service packs, .net, XNA, Steam,...
If it really is something you deleted these things will bring it back, but it is quite likely that your OS went nuts, so maybe the recovery will help or you need a full reinstall.