Computer freezes up in 10.4

Hi Everyone:

I am running Ubuntu 10.4 on a Dell Inspiron 1525 laptop.

After a period of time my computer seems to freeze up. Happens mostly when I'm in a browser such as Firefox or Chrome. It's not task specific. It just happens. When it does happen, I can't click on anything and I can't even click on the icon in the upper right corner to reboot or shutdown the computer unless I press the power button. Once I reboot, everything is fine, but then eventually it happens again and I start the whole process over again.

Any suggestions on what could be causing this? Thank you.

Sincerely,

Mark