Getting an odd error message

[Canadian 2.5RS]

I am getting an error message that is frustrating the crap out of me. When I try to open various applications i get the message "windows cannot access the specified device, path, or file. You may not have the appropriate permissions to access the item." This happens when I try to open several applications. I dont know what to do. The other problem I am having is when I try to download files they wont download correctly or not at all. for example I try to download the software for my canon DSLR and my download stops at about 60% everytime.

I cant even download IE7 (i was going to try to reinstall it).


I think I am going to go crazy!!

UPDATE:

I get the error everytime I try to download a program. The program will download and then when i try to run the installer i get the above mentioned error. I am also having trouble downloading larger files. They just seem to quit at random times.