Windows 7 stops responding when PC is booted

Hey, guys! Anyway, I'm having a rather annoying issue that started a few days ago. What happens is that when I boot up the computer, it works fine until I get to the desktop, in which case I see that loading circle by my mouse and then Windows 7 stops responding. All my desktop icons and the taskbar disappear and all I can see is my desktop background. Sometimes the screen turns black and I can't use Ctrl+Alt+Del or anything. My mouse still moves around, though. I don't remember the exact wording, but the error basically says that Windows 7 has stopped responding but may return in a few minutes (which it doesn't unless I have to wait an obscenely long time). I have to manually shut off the computer and restart it, and then it works fine after I "Start Windows Normally" from the black screen that comes up when you don't properly shut off your PC. So long as the OS doesn't crash on startup, my computer works just fine.

I think I know what the culprit is. I downloaded the free version of AVG and used that PC tuneup thing they have that deletes junk files and fixes registry errors and what not, and the next time I booted my computer after I did that is when this started happening. The thing is that I already tried doing a system restore right before I even installed AVG and the problem still hasn't been fixed.

I also tried verifying that all my Windows files were there with cmd.exe and everything was apparently there. I haven't downloaded any new drivers for anything in a long time, so that's not the problem. I looked in administrative events in event viewer and saw nothing relevant to the issue in today's date. I have MalwareByte's Anti Malware, avast!, and recently AVG, all up to date, and none of them detect anything (which admittedly I find somewhat suspicious as nothing as been found in a long, long time). I really have no idea what the problem is, so any help would be appreciated. Thank you in advance!

Also, here are my specs in case they're useful for whatever reason. Let me know if any other information is needed, though I think I covered everything. I hope.

• ASUS M4N98TD EVO AM3 NVIDIA nForce 980a SLI ATX AMD Motherboard
• GIGABYTE GV-N460OC-1GI GeForce GTX 460 (Fermi) x2 SLI
• AMD Phenom II X4 965 Black Edition Deneb 3.4GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Quad-Core Processor
• G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model
• Corsair TX750W 750-Watt Power Supply
• Western Digital Caviar Black WD5001AALS 500GB 7200 RPM 32MB Cache SATA HDD