|The reason you can't update your virus definitions is because the application that your computer uses to talk to your router beforehand is failing to load. |
Go too the start menu, then the run tab, and type: "sfc /scannow" without the quotes. This will open up the system file checker, which will scan your computer for missing system files, of which POWERPROF.dll is one. It should replace the file with a clean one from microsoft. Let us know if that fixed the problem!