networks are not detected after restarting or shuttin down

hi im running vista home premium and i am having problems with connecting
online on wireless when i restart or shutdown the comp and when i turn it
back on it doenst detect any wireless routers at all i have checked
everything i even reinstalled vista and cleared all files but it still seems
not to work, sometimes after a hour or so of restarting it detects all the
routers around my house which its supposed to do, any ideas why this is going
on and if there is a way around it a easy way cause im not really a computer
person lol??