Have you checked that it's not just a dodgy USB cable? That's the most common problem - try a different one.
If it is drivers, then they should install themselves. There was probably an installation issue. Try the following:
- disconnect the phone from the computer
- uninstall ALL phone related sofware and drivers from the computer
- restart the computer
- restart the phone
If your phone came with PC software, install this - do NOT connect the phone until prompted.
If your phone did not come with PC software, connect it to the computer
In both cases, do NOT disconnect the phone until ALL drivers have successfully installed.