my laptop has built in wireless & does,nt seem to be working

my laptop has built in wireless & is not showing on the taskbar or connecting to my wireless network it had been given a loan to someone & l think they had connected the laptop to a dial up connection l have tried just about everything my network supplier says it seems to be switched off l have contacted the laptop manufacturer l tried what they had told me to press F4 but it did,nt work can you help