Something's incredibly wrong with my computer - Lock-ups, Slow-downs, missing stuff..

First symptom noticed: Lack of things to click on when I right-click something. Just comes up with two menu selection things with arrows on them, as if to scroll through the items in the menu. This was partially alleviated by right-clicking around the desktop (empty space's right-click menu was just fine) a bunch of time and then right clicking the item again. This gets the context menu up, but the default action has disappeared, but its spot is still there, empty, but functional. I thought it was because I installed Unlocker, but uninstalling that had zero effect.

Second symptom noticed: Skype was acting up. Big time. It wouldn't update chats, kept thinking chats had new messages, wouldn't let me kick people out of rooms, and kept saying it was out of resources, despite there being ~2.5GB of RAM free.

Third symptom noticed: Gaming performance plummeted. I was lagging on COD4, which I usually maintain a solid 48-60FPS on, I got on average 26FPS.

Fourth symptom noticed: Things were slowing down and locking up. Opera would freeze up every time I opened a new tab, Chrome would just lock up for no reason at all. WinRAR would take 5x longer to extract files. UAC prompts took FOREVER to come up.

I decided that enough was enough, and decided to boot into Safe Mode. Now it's running slower than before! I cannot so much as load the start menu without locking up or even mouse over start menu items.

I won't rule out a hardware issue yet (perhaps a HDD's failing or something), but it looks mostly like something wrong with Windows 7, or perhaps NOD32 failed me and I contracted some sort of malicious software? I got no clue here.

EDIT: HiJack This isn't coming up with anything, so it might not be anything that gets loaded up that does it.