Your notebook should have come with a backup/restore disk (unless it came to you via a shady source). If you don't have those disks, you basically have nothing but an expensive paper weight.
Advent is the in-store brand of PC World (and there is zero support from PC World). The 5421 is basically a rebadged Uniwill U50SI1 (you should see this printed on the underside of the laptop). I'm fairly certain this is the same as the Gericom Phantom A4 Superlight 53120
, the Gericom website contains drivers and a user manual.
Advent Repairs and Spares:
All official service and support is handled by The Tech Guys (http://www.thetechguys.com/)
, if your laptop is covered under warranty then you need to contact them for repairs.
If your laptop is out of warranty then there are a number of other companies who do either repairs or supply spare parts, here are a selection -
TechnoMart - http://www.techno-mart.co.uk
DriveMyLaptop (replacement drives) - http://www.drivemylaptop.co.uk
Laptop Solutions UK - http://www.laptopsolutionsuk.co.uk