How to troubleshoot a computer

Describing the problem other than just "Hang" would give us some idea of how to help.

Does this happen in games, CPU intensive activities, opening music?
Have you been monitoring the CPU usage during general use and when it hangs.
Have you run benchmarks such as Prime 95, Furmark and such to test the components are stable?
Have you run MemTest to check if the RAM is failing, same with Disk Checker for the HDD?
What is the specs of your machine and how old is it (particularly the PSU and HDD)?
Is anything overclocked?

^Comprehensively this

Give us more information such as the specs of your system and what you're doing when it hangs and we might be able to make an assessment.

its an hp pro CPU with 2GB ram and 500GB hard disk memory. just abt 6months old. opening of internet explorer and some documents are what am doing when it gets hanged

Does it also take a very long time to start up? You could use memtest x86 and chkdsk to rule out ram and hdd.