New Hard Drive, Can't Open .exe Files

[GoPitt]

Ever since I got my current Dell computer, I have been plagued with problems. The computer crashed multiple times, the ethernet port on the back broke, and eventually after all that was straightened out, the hard drive crashed. After replacine the hard drive and reinstalling windows vista, the computer seemed to work alright. However, I was not able to run any .exe files as every time I did, I was prompted with a "file corrupt" error or something of that nature. I was able to get windows 7 ultimate for free from my school and thought that this might solve the problem, but I was wrong. The computer updated fine and is now running windows 7, except now when I click on any .exe files, I am prompted with an "open file- security warning" box that tells/asks me "The publisher could not be verified. Are you sure you want to run this software?" When I click "run," the small loading circle thing spins for a few seconds and then nothing happens. I am new to forums but I am absolutely desperate. I can't install mozilla, flash, anything. I will provide any information necessary in fixing this problem. thanks in advance!