In wireless networking, a location within the coverage area where a signal is not received. Dead spots are typically caused by physical barriers (such as buildings or concrete structures) that absorb or reflect radio or microwave frequencies.
The receiving station must relocate or the barrier must be moved if the station is to receive a signal. Dead spots can also be caused by high levels of electromagnetic interference (EMI) from heavy machinery (such as motors and generators) or broad-spectrum sources of radiation (such as microwave ovens).
In these cases, too, the solution is to relocate the receiver or eliminate the source of interference.
If you have Dead Spots in your wireless network you shoud install wifi range extenders. For better performance use this from Google PC:
Wifi extenders to eliminate dead spots.