computer problems

What's up with my computer? It seems to have a limit on things that can be opened before it becomes nearly nonfunctional. Tonight I opened tons of image pages on Flickr, and at a certain point, it was so busy that it couldn't do anything. The drive kept crunching at full blast, and it was sometimes minutes before it could refresh a page or switch windows. I've also had this happen with Photoshop, and MS Office fills it up pretty quickly too. When it gets to this point, it doesn't matter what I shut down, the box seems to enjoy replaying these images over and over in its head. Tonight, I shut down Firefox, and it returned to normal, but if Photoshop caused the problem, a reboot is required.

Can anyone tell me what's going on here?