Update your wireless drivers, even if it's brand new they could be out of date.
Another problem could be you're using the wrong wireless type (eg. your router might be wireless G but your laptop is trying to use a different type, such as wireless N) but I think that's relatively unlikely as any decent PC should pick that up and automatically use whatever is available.
It could be interference between your wireless network and someone else's close by (Wireless networks normally have channels, check on your modem/router). This one seems most likely to me, perhaps your new laptop uses a different band of wireless which is interfering with a neighbours connection?