Inspiron 1545 Diagnostic test error 0146

My screen froze whilst on a website and ctr alt del would not work so i pushed the on button to restart, the dell screen comes on and the bar loads but nothing further after that, i have tried everything i can think of, i have tried to repair windows using f12 on the boot screen and whilst it recognises the cd is there and begins to load it then just freezes. If I reboot without the cd it stops on the message "missing operating sys".  I followed instructions on here to do the diagnostic test and as it gets to test the hard drive and the above error comes out, anybody able to help as Dell website does not recognise my service tag so I can email them to discuss. just went to check I havent done something before taking it to a computer support store/sending it back.

many thanks in advance.