It is an issue with the driver for the Wifi card for the Dell Insperion series. I had the same issue with my dell, tried everything, but still kept on loosing connection or the speed would drop to 1 MBps. Was very frustrating.
So try uninstalling and reinstalling the Wifi drivers. Dell uses 2-3 kinds of Wifi chips, so make sure you download and install the right drivers.
2) In the Wifi Adapter settings, make sure you are configured for the 2.4 GHz only, sometimes the dual 2.4/5.0 will make your adapter go nuts.
3) On the router also, make sure that it is just one of the frequencies that the router operates on. Only latest AC routers are capable of really running both the 2.4 &5.0 spectrum's at the same time without any issues. If you...