my sons got a compaq pc pentium 4 256 RAM that was working fine until last week but suddenly became very slow (mega slow).I thought it was about time for a format so tried reinstalling xp but it has now taken over 4 hours and still not completed installation.
By judging the amount of time its taken i asume theres still something else wrong with it thats beyond my very limited pc know how.Anyony got any ideas,cheers

Google "Windows XP tips" people ask that question all the time and you will find an answer fast. A utility to play with would be MSCONFIG. Basically click START then click RUN...now in that little window type msconfig and then OK.

A new window will open. The last option on the top menu is STARTUP. That is a basic list of programmes that start everytime you start the pc. You can use google to find out what each is. By unticking the boxes you effectively stop the progs running. The progs will still run when you want them too.

I haven't reinstall an operating system is years due to a problem. There is always a fix (most of the time). You can also research services you can turn off too. Remember google, it's a gr8 tool.

Usual things...virus scan and anti spyware Good Luck

You could do with more ram. 512 or above will help.

It could be you BIOS to try if it is go restart your pc and keep pressing F2 (it may be diff on ur pc but its normally F2) and once your into your BIOS load optimized defaults and press F10 and save it and restart.

Ronster dont start messin about with the bios on your boys pc if your not sure about settings as you might find your self in trouble. go with welshwolfs advise and use msconfig.