Option 1. Take it somewhere to get fixed ~$200
Option 2. As Madaz said, load into safe mode and try and install AVAST or MalwareBytes...I dont suggest AVG, I see too many PC's at work with this installed, and it makes more issues then it fixes...if it fixes anything at all.
Option3. Use another pc that has a decent Antivirus system and up to date, suggest BitDefender, Kaspersky, or TrendMicro. Plug your Hard Drive into that system as a secondary and scan with Antivirus, hopefully that will fix the problem, but by the sounds you have a more serious issue.
Option 4. Find out what infections you have and google the removal process for them. Will leave windows some what shagged, as the newer smarter virus's hook into windows real well, and when you remove them you tear bits of windows out as well, so this is more a temporary fix...similar to Option 3.
Option 5. Back Up & Reinstall. Fail Safe method.Get an External Hard Drive, or another Hard Drive in the PC, Back Up to it - Copy Files, ie Documents, Movies, Music, Etc. Unplug Ext Hard Drive/Hard Drive, Reinstall Windows, Install Drivers, Install Windows Updates, Install a Good AntiVirus System - Refer to Option 3, Update AntiVirus System, Plug in Ext Hard Drive/Hard Drive, Scan with AnitVirus System, and then copy your data back across.
Option 6. Get me to do it...for beer + cost of AntiVirus System ~$35