Ever wondered how long was your computer switched on ?

View XP System Uptime

To view the amount of time that XP has been running with out rebooting or restarting the computer:

1) Open the Command Prompt (located under Accessories)

2) Type 'systeminfo' (without the dashes)

3) Once the system has finished gathering the information, scroll up and the time is displayed in the System Up Time field.

As you can see, running systeminfo also gives a lot of useful information.