Wireless connection dropping

I have a Inspiron D 1721. I use Vista. I've had it for a while and up until now I've had problems. When I was in CA I could connect to the internet wirelessly with ease. I cam back home and was able to connect with ease again. I had a motherboard problem and it was scent to Dell to fix. When I got it back I as able to connect but the connection dropped around an hour then if I waited it would come back on.

 Now if it drops I have to restart my computer in order to on online. 

My brother also has a Dell but his is working fine. No internet problems at all.