WNR2200 router showing limited access

hi there!

I'm new to these forums so please excuse me if this post is in the wrong place but still, thanks for the help in advance!

Basically a while ago at home we had a router set up normally (Lan > modem > router > into our desktop. THINK that's how it was but not too sure)

Then about 3 weeks ago we had our desktop wiped and reinstalled with windows 7. At the same time Dad 'updated,' our router to the WNR2200 but also added a LAN card in to our desktop PC so now, we have a LAN cord going into our modem, into our desktop PC which transmits to our router which then obviously sends out WiFi; but here's where the problem occurs.
On my laptop, HP with Windows 7 and our desktop PC (sometimes) the internet becomes really slow and connection drops and eventually it shows limited access and all devices suffer from slow internet.

I've tried getting another IP address on my laptop (using the ipconfig/renew thing) and I've searched other places and its mentioned DCHP or something like? :confused: but my attempts have come to no avail!
I'm not realllyyy that good on computers but I could probably find my way about...

I'd just like to know how to make the internet consistent and reliable so i don't have to constantly connect and disconnect to get it too work...

Any help would be great! Thanks :D