A bug or virus is preventing me from opening my Spyware and my Malware programs.?

Even in safe mode I cannot open these programs. I downloaded Avast and used it, but the problem persists. I tried reloading Norton Utilities (which I took off because it made things slow) but it could not load, and would not let me load it in safe mode. The problem is inconsistent. Sometimes it freezes the screen and I have to manually shut down. My home page is always changed to Google. I want to buy a new antivirus but am afraid I won't be able to load it. Thoughts? Thanks. Malcolm