Hello Neil, welcome to Vista forums!
I have done many "System Restores" and it usually finishes and re-boots in less than ten minutes.
If Dwarf's suggestion about "SFC" doesn't sort it out for you, then have a look at this.
Below are the directions to do a "Factory Recovery" directly from the "Recovery" partition
added by HP at the factory.
Be advised that it will bring the machine back to the point you first took it of the box.
HP Recovery Center
The "HP Recovery Center" will give you the option to send to backup anything you
don't want to lose, so have backup media available to use if you choose this option.
With the machine off press the power button, as soon as you do that start tapping the F11 key.
That should take you to the HP Recovery Center. When there just follow the prompts.
It is pretty much self explanatory. From the time you boot into F11 (not counting
any backups you choose to make) you should be back on a working desktop in about
30 minutes. After it restarts just follow the prompts again to finish the process.
If your first option is system restore select no, which should take you to system recovery.
You want to try system recovery not system restore, unless you have good restore points!
Keep us informed!