You can get the XP numbers from the authentication sticker pasted to your computer or from the original packaging. If the OS was preloaded on your PC, you should still have a sticker, otherwise contact the manufacturer, call MS or get a legal copy.
Solving problems that are seemingly random or intermittent in nature can be difficult. As a start, try shutting down your system. Let it cool down for a while with the power disconnected.
When cooled, plug in power, start back up and note any strange behaviour. Where/when/how does it fail?
For further help, you should provide some basic info about your PC (model, peripherals, OS, etc.). There are at least 9 variants of Win XP. Which one are you using?
The more detail you can provide, the easier/quicker it can be to solve your problem.
Dell