Duff computer or maybe just a failing hard drive

I have been given a Compaq ipaq to look at that won't boot into windows 98, I strongly suspect that the hard drive is on its way out because sometimes it is detected by the BIOS and othertimes not. When it is working the whole pc runs so slow its unbelievable, the scandisk when loading windows took over 10mins. It is a western digital and has hardly been used. I have checked the memory which tests OK.
Have you any other suggestions or do you agree the HD is failing?

Please check out this thread which is a "Read" thread at the top of the storage and networking forum. https://www.techspot.com/vb/topic7602.html

If you are in a HUGE hurry and don't have time to read the first post in that thread. Get the WD diagnostic thing here: http://support.wdc.com/download/index.asp#dlgtools