It could be an interference problem that's causing the signal to be lost. See if you can change the Channel number the router broadcasts on by going into its "wireless" settings. The default setting is usually either "6" or "11" so try one of these, or the other of these if already on 6 or 11.
Avoid 12 and 13 as some wireless adapters are designed not to connect on these frequencies (which are illegal in some other countries). Also avoid 1 and 2 which many other wireless devices, such as mobile & cordless phones, tend to use.