Sounds like your Java software got corrupted. First thing is check to be sure your hard drive isn't failing. You should always mention model PC and version of Windows in your posts. But if this is typical Dell, reboot and press F12 before Windows starts to load. Run the hard drive tests. Copy any error messages and contact Dell for replacement, if you're still under warranty. And back up your personal files to CD right away.

If no hard drive errors, when you're at the desktop:
click start>run
type in: chkdsk c:/f
click ok
You'll get message offering to run chddsk at next boot. Press y to accept and when back at desktop, reboot.

Then you can go here for the latest version of Java software:
http://www.java.com/en/download/index.jsp

Ron