After putting in new hardware my computer fan has been spinning faster.
Also, if i put my hand behind my tower it is very hot.

I dont know whats the matter.
I've cleaned it of dust multiple times and that does nothing.
Im wondering how to fix it.
I only really notice this when I would start a game on my computer, like when Im putting stress under it.
For example, I would start up World of Warcraft and the fan would gradually get louder and louder. Untill its at the point I cant take it and must turn off my comp or exit the program.
Another thing that happens is when I exit the program I get a blue screen error, but only when the fan is spinning loud.
Then, when I turn my computer off and turn it back on the fan is spinning like a bat out of hell for approx. 3 sec.
Can someone please tell me whats the matter, or what could be happening.
Should I just buy a new fan and replace this one?

What hardware did you install? Did the newly-installed hardware physically obstruct the free flow of air within the chassis?
Judging from your description, whatever you added is generating enough extra heat (or blocking the airflow enough) to cause the fans to kick up a notch in an attempt to keep the temp at a safe level. The fact that the problems really exhibit themselves when you're gaming (games drive a system pretty hard) indicates that you may need to beef up your case-cooling scheme.