Open the Utility folder, inside the applications folder, and launch Disk Utility.
Select your HD in the LH column and click on Repair Permissions.
Once completed, try to launch one JPG and see if it made any difference.
The fact that the other account is unaffected would normally mean that the software or system was not damaged.
By the way, OS X has a series of versions from 10.1 to 10.4. It could made troubleshooting a little easier if you were to mention what flavor of OS X you are running.
Okay, I had a huge batch of pictures to look at... probably close to 200... and selected them all and clicked "open".
My computer buzzed and hummed forever, longer than usual, but looked like it was doing nothing so I restarted it.
This time, the user account won't let me open .pdf files. jpeg files or .txt files. Another user account, which doesn't have access to the Internet, is unaffected. When I click on the files in the troubled account, the "working" cursor appears and the program loads, but the file never opens and the computer never stops trying to open it. Something is really wrong. I let a single .jpg take half an hour to open and it never did anything.
I've restarted it a number of times but the problem won't disappear.
Help would be greatly appreciated. Thanks. I'm on a MacOSX G5.