With PCWorld you have NO RIGHTS WHAT SO EVER.
Or so PCWorld would like you to think, you have every right available to you.
Do you recall the exact date or close enough month/year? if it is under 12 month old the store has to repair it at no cost, if it is a fault.
The Sale and Supply of Goods Act 1994 gives you numerious rights, write them a letter, send it to the store and also CC a copy to DSG (Dixons Stores Group) this is PCWorlds headoffice.
Be prepaired for a long fight though, it will most likely be not easy what so ever, numerious people have similar woes with PCWorld/Currys/Dixons as yourself.
And don't expect a refund what so ever from them, unless you get a district judge to order them to do so
Sorry for the negative post, but its not going to be easy for you.