Windows Explorer freezes on log in

I am unsure what section to put this in, so I apologize if this is in fact the wrong forum.

My problem is as stated - as soon as I log in on my desktop (I am on my laptop here) Windows Explorer freezes. Nothing on the taskbar is clickable - the time on it does not move. Nothing on the desktop is clickable, either, but despite this skype, one of the programs that automatically loads when I log in is accessible via alt-tabbing to it; it works just fine. If I hit ctr-alt-del, I am able to log off, change my password and so forth, but if I open the task manager (either by that method or by ctr-shift-escape) the task manager is likewise frozen, unable to click anything on it. At no point however does it go pure white and prompt a message that informs me it is unresponsive, giving me the option of restarting it or waiting for it to respond.

This started today. It has never happened before on this computer. It is, as far as I can recall, running Windows 7 Home Premium 64bit.

Any help would be greatly appreciated.

I've installed a number of different things on the computer, but most are pretty mundane - some games from Steam, League of Legends, I installed a program from the external hard drive I purchased a few years ago on it. I also installed a sticky note program as well that I've been making use of in the last month or two.

Nothing else immediately jumps to mind - I have been letting windows automatically update, and I haven't installed anything as of late, nor can I recall any recent updates in the last few days that are worthy of note. I will note that start up for the computer has been getting slower and I have been meaning to clean it - I use the task manager to shut down the external harddrive's program each time I log in because it makes it lag something fierce, but recently it's been laggier than usual.

That's about all I know of.

The system restoring appears to have done the trick, but I will definitely utilize the rest of your suggestions to clean my computer up, and set up manual system restore points. Thank you very much for the assistance.