Some laptops have a physoical switch, some use a series of keystrokes and some have software utility. As you have an Advent it could be any one of those three. (Because Advent doesn't have a single maker as it is an Own Brand of DSG - Currys/PC World.)
Try reading the manual, or you may have a guide on the laptop itself. Failing that (and I have not come across manuals that do not tell you help to switch wireless on.) try DSGs technical site www.thetechguys.co.uk
T
November 2008