It's not clear if you've upgraded to Windows 7 from an earlier operating system but, if this is the case, make sure you have the latest drivers for your Wireless Network Adapter. These should be available on the HP site.
Keep any cordless or mobile phones well away from either the Router or the Wireless Network Adapter (Laptop).
You could also try changing the Channel number in the router's wireless settings. Most routers use either "6" or "11" so try these or, if already on one of these, try the other.