[damien c]

ok let me get this straight

blue ethernet cable from modem in to the internet port on the back of the router
then ethernet from the router to the main desktop pc
then wireless to the laptop

is that right?

if so does the main pc (wired) loose the internet aswell?

if so if you use ethernet from the modem to the main desktop pc does it still loose the connection?

if it does then there is a problem with the modem if it doesn't try the laptop wired directly to the modem if that doesn't loose, the connection then there is a problem with the router, it may be down to the settings or it could be a hardware fault on the router.
but your first port of call is to try the pc/laptop wired to the modem process of ellimination, as that will tell you what is causing the problem.

if it is the router take it back to where you bought it from and ask for a exchange or ask them to test, it question is where did you buy it from? and how old is it? as this will depend on what they will do with it.
I had a very similar problem when connecting a ps3/pc/360 to a belking 54mbps router and the router would die if i tried to use the, ps3 and pc on the internet at the same time, i had to go out and buy a netgear which solved the problem untill i got rid of me ps3/360 now just have me pc wired directly to me modem faster and allot safer hope this helps and hope it is not to confusing.

also there is sometimes a rest button on the back or bottom of the router have a look se if it has one and if so give it a try after reseting it.