Dell Inspiron N5110 :: Hard Drive SMART Short Self Test Failure

I have a Dell Inspiron N5110. The Warranty ran out in July of last year so for some reason I cannot email technical support directly.I ran the Dell PC Diagnostic test earlier today, all of which passed with the exception of the SMART Short Self Test which failed. Apparently my hard drive is "operating outside of normal parameters and should be replaced". I tried this twice, once with the Dell diagnostic software installed on my laptop and once using the downloadable diagnostics from the Dell website, both had the same outcome.  

I then tried the system diagnostics accessed via the F12 key on system startup. Again all passed but the hard drive test which would not run and provided the following message:

Error code 2000-0142
validation 12985
Msg Hard Drive 0 s/n (omitted), self test unsuccessful status = 7

I have read around on the support forums that the next step to try is removing and replacing the hard drive then re-running the diagnostics. If this does not solve the issue and I have to replace the hard drive does that mean I will need to buy a new copy of windows to install on the hard drive, as my laptop came with no disks? I have backed up all my important files but obviously not any programs.

what my next steps would be and what the process is should I have to replace my hard drive? I am a "noob" in this area and don't want to spending uneccassary money on parts that don't need to be replaced or buying software I don't need to replace as it is already available if you see what I mean?