Moved to Malware Discussion > Home User Assistance.
1st thing to try, power machine off without clicking anything. Power on into Safe Mode by tapping F8 repeatedly while booting up and then initiate System Restore to go back to before it all started.
if successful turn System Restore off and then back on again in order to delete the infected resatore point.
2nd thing to try is this excellent removal guide: http://www.bleepingcomputer.com/virus-removal/remove-windows-pc-defender
Windows PC Defender and PC Defender Plus are two different programs, by the way. PC Defender Plus scam has been released just recently, by the way. This is a rogue antispyware program that attacks many computers and reports many fake infections that aren't real. You should get rid of this scam as soon as possible using McAfee. Actually, I myself use McAfee and think that this is a powerful tool to remove malwares. Alternatively, you may use some other programs of your choice. For example, a friend of mine has the same problem and he found another program that fixed his PC from this virus. MSE or Avast should be helpful too. There are some principles of how exactly to run the security software, since PC Defender Plus scam often blocks launching legitimate security applications. Please find some useful instructions in this guide -
And this video is also a good example:
BleepingComputer guides are extremely reliable and thorough. This one wasn't there when I originally searched for it.