I have a Dell XPS 710 running Windows XP Pro.  The computer has suddenly started shutting itself off unexpectedly, sometimes after 5 or ten minutes, sometimes after several hours, sometimes I shut it off when I'm finished using it.  It has shut down by itself off 4 or 5 times within the space of one hour.  I've tried using system restore only to find all my prior restore points unusable.

Any suggestions?

   It sounds like your power supply is going out.  Try replacing it.

I'm not exactly a fan of restore points. I've never had one yet that could be used!

Re unexpected shut-downs.. Had a similar problem with a friend's lap-top. Turned out to be a power supply problem.

And on the side issue raised by Alanturk, I have never relied on the Windows System Restore. Used GoBack for a long time before it became part of Norton and I since that 'take-over' I have used RollBack RX from Horizon DataSys. It isn't cheap but it is very reliable with a friendly user interface. For instance, you set when you want the program to take a snapshots of the system state and it has saved me a 'serious headache' on a number of occasions. Their technical support is superb.

Dickiesam

Quoted from edkraft I have a Dell XPS 710 running Windows XP Pro.  The computer has suddenly started shutting itself off unexpectedly, sometimes after 5 or ten minutes, sometimes after several hours, sometimes I shut it off when I'm finished using it.  It has shut down by itself off 4 or 5 times within the space of one hour.  I've tried using system restore only to find all my prior restore points unusable. Any suggestions?

You might also consider overheating. Take the lid off and look under the fan on top of the cooling 'radiator' (ignore any fans in the power supply or fixed to the case itself). Often this will concentrate dust between the vanes of the radiator. A quick blast of air (use a drinking straw if you've nothing better) should clear the dirt and restore normal cooling.