Hi - I have a Dell Inspiron E1505 with Windows XP. Within the last few weeks the computer has started rebooting without warning at random times. I have not been able to find any common link with what I am doing when it reboots. I have updated Windows, I have updated and run virus/spyware, and I have run a system diagnostic assessment - all have come back clean. Yet, the computer has been on for 2 hours tonight and has rebooted twice.

Any ideas? Thank you!

right click on mycomputer /go properties/advanced /startup and recovery/ settings / and on check auto restart ,,this then should give you a BSOD error message ,copy down the stop error message code #'s and post them back here .it will look something like this .
"Stop 0x0000000a(0x00000029,0x00000002,0x00000000,0x80466d7b" error message after Windows is already installed

i had a similar problem to this a while back.
I would be half way through doing a task and the pc would just reboot by itself.
What i found that it was a faulty memory stick.
If you have 2 512mb or 2 256mb memory try to take one out and see if the problem stops or carrys on.
If it still keeps rebooting swap the memory stick in the pc for the one you took out.
I hope this makes sense to you
Good luck