I have a Vaio laptop, about 18 months old. Last week, after I knocked it (tripping over the lead) it froze up. I rebooted and got the message 'operating system not found'.

After looking at some answers on this forum (thank you!) I switched it on again and pressed F2 to access the BIOS and it said 'Hard disk: none' I tried this a few times over a few days and it always said the same.

I took the hard drive out and tried it in a hard drive dock, plugged into my old laptop via a USB. It does not detect the hard drive at all. I'm guessing from all this that I damaged the hard drive when I knocked the laptop.

I'm looking for some advice on what to do next please. Are there any drawbacks to me simply buying a replacement hard drive (I can buy the same make and model - a Seagate Momentus 5400.6 on line) and fitting it myself?

The current drive is 320GB but I thought if I'm going to replace it I'd buy a 500GB one (otherwise exactly the same model). I think I've read somewhere that I shouldn't buy bigger than a 500GB for a laptop but would appreciate feedback on that too.

Also, does anyone know the odds of getting the existing hard drive repaired? Recovering the stuff on it is not a major problem as I'd backed up most of my files to an external hard drive (though I'll lose some recent stuff), and I made all the recovery disks when I first got the laptop.

My main concern is more about whether to try to salvage something from the old hard disk or just buy a replacement.

Thanks