I have a dell 1525 which has stopped booting.
It instead makes a high pitched intermittent whir and say "internal hard drive not found", I'm not particularly hardware smart...
How can I solve this issue?
Best bet is to log a support ticket with Dell - there are a few possible causes.
If you are happy with taking it to pieces, you can check the cables are correctly seated (give the cable to the hard drive a push into the socket at each end) but most likely is that the hard drive has died - in which case you'll need a new one.
If you go into the BIOS configuration, usually while the computer is initially powering up and by pressing F2, F10, or Esc (it will say on the startup what key press enters setup) You should be able to view disk drives.
Does your drive show up in the BIOS? If it does, it seems like it could actually be a software corruption, if not, my best guess for you would be that your harddrive died. How old is your Dell 1525?