I hope it wasn't a scam you got into. Sometimes when browsing the internet a popup will appear saying RED ALERT Your Computer is At Risk, or some such rubbish with a button to click to remove the risk and scan your system. If you click the button, it appears to run some sort of scan and then advise that you have a number of errors which you can have them remove for $50 or $75 bucks. If you decline, your computer will lockup and unbeknownst to you they've installed an empty file which acts as a conduit for a number of their associated companies to use to access your PC and create havoc. Some of the companies are hackers armed with viruses.
I went through that on my old PC last year. I was able to do certain things online as usual, but the one thing I couldn't do was any sort of web searches. No search engine would work. I wasn't even able to launch my browser until my ISP gave me the IP address of Google which I was able to use as my browser homepage instead of the usual www.google.com.
Finally about two months ago, when my wife decided she didn't want to use my new PC and wanted to continue using the old XP machine, I paid Microsoft $99 for a 30-day service agreement and they commenced looking for the problem. It took them a total of 30 hours over three days to get it sorted out. Each day a different level technician had control of the PC. Finally after six hours on the 3rd day the level 3 (the highest) tech ran a special scan which uncovered two viruses which had resisted all scans to that point.
He then downloaded and installed a small program called tdsskiller which is a freebie from Kapersky Lab. http://usa.kapersky.com/downsloads/tdsskiller
which he then ran. It detected and removed the two trojan viruses. The computer now runs like new, faster than ever, it seems to me, and everything works fine. I've since ran that tool about once a week just as a precaution. And I've installed it on my new Win 8 PC as well.
I hope you find a way to get your PC running again. You might then consider installing that "tdsskiller." It's a tiny program that works wonders.