computer freezes after 1 hour of use

[jaddoomran]

Computer specification: 1Gb of random access memory (20% is used); 25GB of free storage in the hard drive; purchased September 2004(Dell Dimension 2400); Intel Pentium4 2.80GHz CPU; Ubuntu 9.10 operating system.

The problem: After about 60 minutes of use, the computer becomes unresponsive excepts for the mouse pointer. I can only restarts by turning it off from the power button; then again it freezes after 5 minutes of use. 

[Geek-9pm]

Welcome!
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What you describe is classic overheating. Check the fans.
 Have you ever blown out the dust from the computer case? How about the power supply?
Even some techs that should know better do not notice that the power sypply fan is stuck. No as rare as you might think.