Until it's determined if/what the virus is, it's hard to say what's yet to come. Doing a full system scan for malware/viruses is the first thing you should do anytime your security software doesn't start.
Try running Malwarebytes in Safe mode while disconnected from the net.
You can d/l and run MS Malicious software removal tool:
Download details: Microsoft® Windows® Malicious Software Removal Tool (KB890830) x64
You can install MS Security Essentials which combines defender functions with an AV.
Anti-Malware, Virus, Spyware Protection | Microsoft Security Essentials
If it is a deeply embedded virus you may want to consider using Norton Power Eraser, it also now has a rootkit scanner:
http://security.symantec.com/nbrt/npe.aspx?lcid=1033 Quote:
Because Norton Power Eraser uses aggressive methods to detect threats, there is a risk that it can select some legitimate programs for removal. You should use this tool very carefully.