I have seen this from Malware, but I have also seen it from registry errors, and in one extreme case, anti-virus definitions gone wrong. The anti-virus thing somehow had a corrupted database and was identifying every executable as a virus. Getting into Safe mode can get through just about every cause. I have also seen some Malware (particularly the XP Antivirus variants) run in safe mode and prevent removal systems from running.
I'm working at the moment, so I can't put too many details in here right now. (I'm waiting on a server to install software at the moment.) However, I'll give you some pointers that might help.
First, if you can get into safe mode, but the problem is still there, then remove your hard drive and hook it to another system using an external USB enclosure or a USB adapter. These are usually available from a Fry's or Microcenter for about $20. Use the other system to scan for malware/ viruses. Once scanned, put the hard drive back in the original system, but power it up DISCONNECTED from the Internet. (Many Malware programs will set up the registry to reinstall the Malware from an Internet source.) Then try to scan the system for Malware again. That should take care of registry entries from the Malware.
If this doesn't fix it, then it is likely a different source. An OS reinstall might be the only way around it. In which case, use the USB adapter from the previous paragraph to save off your data before reinstalling.
If you don't have another system to use to scan or save, find a friend or family member who can use theirs for this purpose. If you don't have that, then take it to your local computer tech. It will cost, but there's not much of another way.
(Now off to troubleshoot a network switch. I won't be able to respond for a while.)