Just a little info if your computer gets hijacked and you can't even get on line or open any of your files. Somehow (and I am extremely careful) the AV Virus got into my computer. This is the one where they lock your computer up and offer to clean it up if you pay them money. My virus programs couldn't remove it after scanning. I was lucky I had my laptop and went online and googled the problem. So here is what I did.
I have XP so I have system restore. First shut down your computer, then as it's loading quickly hit F8 to open in Safe Mode. From there you can restore your computer to BEFORE the virus got into your PC. Try this before calling for an expensive techie. As you can see, I'm back on line.
If you don't have system restore then maybe it would be wise to try to find out what you could do if it happens to you now, before it happens.
Hope this isn't too confusing and that it helps out IN CASE.