System running strangely slow

Starting a few weeks ago, my system started suddenly running very slowly (e.g., taking 15 minutes to shutdown). But it's oddly intermittent—sometimes it seems to run normally, and sometimes (like this morning) it takes quite a long time to startup and when it does, Aero is suddenly disabled.

What's even more odd is that my computer can still run games fine, though I've sometimes run into issues when I try to exit them.

I've run a complete system scan with Malwarebytes and Microsoft Security Essentials. I did a full chkdsk and repair (found a few bad sectors). I did a Memtest86+ and found nothing. I did an /sfc and it also found nothing (though it failed to run properly a few times before I got it to complete). I updated my drivers for both my ethernet adapter and my video card.

I'm completely at a loss for what seems to be causing my system to behave so badly.

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 7 Professional, Service Pack 1, 32 bit
Processor: Intel(R) Core(TM)2 Duo CPU E7300 @ 2.66GHz, x64 Family 6 Model 23 Stepping 6
Processor Count: 2
RAM: 3070 Mb
Graphics Card: NVIDIA GeForce 9600 GT, 512 Mb
Hard Drives: C: Total - 953864 MB, Free - 614201 MB; E: Total - 238471 MB, Free - 92898 MB;
Motherboard: Gigabyte Technology Co., Ltd., EP45-UD3R
Antivirus: Microsoft Security Essentials, Updated and Enabled

Attached Files

Image may be NSFW. Clik here to view.	dds.txt (17.9 KB)
Image may be NSFW. Clik here to view.	DxDiag.txt (39.5 KB)
Image may be NSFW. Clik here to view.	hijackthis.log (8.4 KB)