I recently fitted a 160Gb hard drive to my sons computer, which previously had a 80GB drive. I used the Seagate Disk Wizard, and  during the process I was asked that as it was a large capacity hard drive and the computer could only handle up to 130Gb 'did I want to fix the problem' I clicked on yes, but afterwards it only recognised the drive as a 31GB drive. How do I access the other parts of the drive please?

   Did it divide it up into two partitions (or two drive letters)?  From your description that is what it sounds like happened.  One of them would be 130gb and the other 31gb.  But the size problem sounds more like a limitation on the BIOS which I would not think could be solved by splitting it up into two partitions.
   I wrote an article about hard drive size limitations in our newsletter, Ray's Computer Tips.  It is in issue 10 at http://superwin.com/RaysComputerTips/Issue10.htm#tech  Maybe that will help you.

As far as I can make out it has only one partition, but it is the smaller of the two that is recognised. I will ned to look at his machine, to check out the tips you gave in issue 10. Will reply again when I have had chance to do so