Computer crashed because of 2 antivirus installed

Hello,
I had Avast in my computer for a month and I just wanted to have k7 in my computer, instead.
But I did not uninstall Avast when I was installing K7.

After a minute or two-
1. None of the applications are opening
2. Any .exe file is not able to open.
3. Unable to open command prmpt or regedit
4. Unable to uninstall any of those anti viruses.

Kindly help me...