After upgarding the firmware, did you reconfigure the router with new settings?
If so, try with the channel:11.
I just wanted to know what kind of wireless adapter is in use?
Also since in wireless connection its dropping, it might be a problem with wireless adapter.
So try to connect to some other unsecured wireless network and check the connection is stable or not. If it is stable,then there is some problem on router.IF it is not stable,then there is a problem with wireless adapter.update the driver for the wireless adapter.