Dell Inspiron N5010 :: Has Locked Up Continually From Literally Day One

I bought my Inspiron over the telephone direct from Dell about two years back on the strength of my satisfaction with a Dell PC some five years earlier.  However I have been so disappointed with it and wish I'd bought a cheapy somewhere.  It continually locks up with the hard drive working away on goodness knows what - this can last from a few minutes to leaving it running all night and it will still be locked in the morning - the cursor actually still moves and you can move between open pages but that's it.  I wrote three recorded delivery letters to Dell which were ignored. 

On line they run through a test and declare it is all operating fine, 'that's it', no problem!  I paid £50 for a professional to look at it and he suggested we reload the software.  This was supposed to be held in a seperate protected part of the hard drive (as it did not come with software discs) which, after talking to his contact at Dell, he confirmed didn't exist!  To cut my losses he arranged for me to buy, more money, a software disc from Dell that he later re-installed for me.  The result was absolutely no improvement.  I know a few computer 'fans' who have all said 'I'll have a look at it' but all have been baffled.  So I have continued to suffer this appauling performance that can lock up sometimes every couple of hours, sometimes every couple of minutes, it can even be locked when I first start it and it then merrily plays with itself for as long as it fancies.