Just in the past few days as I have been using my PC I have noticed that after about half an hour, for some reason I get immense slowdown. Most often I have noticed it occurring while on the Internet and Firefox will stop loading pages (but not a network issue). The one major indicator that this is happening is that the HDD light starts blinking rapidly and continuously, more so than the intermittent flashing of regular use. If I try to shutdown the computer or restart it either takes forever or will not do it altogether, often while flashing up a screen that says "x program is preventing you from shutting down".
I am running Vista 64 and I have no idea what is going on. I have not loaded any new applications that I can think of in the past few days that would explain this behavior. Any ideas on what might be causing this? I can post the rest of my specs on request. Thanks in advance.