The following Registry key is where apps tend to be disabled by viruses...
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\RestrictRun
If you find Malwarebytes, Spybot Search and Destroy, and AVG9 in there, delete them. In fact, the entire RestrictRun key is normally not present on any healthy computer. Group Policy in some domains will use this, but home computers won't.
You have to reboot for changes to work. (In a domain, GP will reapply at reboot.)
If you can't run Regedit, then search the internet for...
re-enable registry portable
...for a utility that unlocks Windows features.
i believe RootkitRevealer can do a good job. If not, running it again will tell you it's not gone yet. That would confirm a rebuild would be necessary.
Panda also has a free rootkit tool. i would try that before rebuilding.