My computer won't let me change any settings

Hello,
Hello,
Hi I have a problem with my computer. I use windows xp and for some reason when I try to change any settings.. A box comes up telling me application is not found.. That goes with EVERYTHING except when I click a program to start.. a box comes up asking me what I would like to run. But if the file I want to change is not there then I cannot go there. For instance my sound does not work and when I go to control panel > audio device and sound options it gives me a few more options like (Change settings) and when I click it the box comes up saying it cannot be found. How do I fix this?
If you need more information to help me figure out the problem please announce thx.