Unable to play video+Connection fails

I have got this ADVENT laptop which i connect a wireless internet connection
using linksys router, currently i receive internet connection but problem
comes when i'm trying to play video using window media player, Connection
fails (both from laptop and desktop computer) and i'm no longer receive
internet connection untill i switched off the broadband adopter and linksys
router adopter then when i switched again on and that's internet connection
comes back.

when i play just normal music (not video) on laptop (using wireless
connection) everything is fine. so i'm not sure what is wrong!!

Also when i play music or video from another computer (desktop computer)
that is in the same network everything is fine no problem.

The following is details of the router:

Router: Linksys wireless-G 2.4GHZ (802.11g) Broadband router with 4 ports.

NB: This connection is security-enabled wireless network.

Please help me on this problem.