aces77

**Please bear with me as i am totally dumb when it comes to technology**

I have a desktop computer, two laptops and a router. My computer is connected to the Internet through a usb modem.
Two days ago i had both laptops and my computer connected to the Internet. I got a tech guy to set everything up for £30 ($60). Now I think Ive totally messed everything up.
I was trying to connect my ps3 to my router, so i messed around with all the network connections. Now nothing works anymore. Ive followed the manual that came with the router, but nothing works. My computer is now connected to my modem through a usb cable. But when everything was set up two days ago, the guy took the usb cable out and connected everything using ethernet cables.
I had my modem connected to the internet port on my router and my computer connected to one of the lan ports on my router and everything worked perfectly. Now when i make those same connections, nothing works and i cant even connect to the internet from my desktop computer, without using usb.
I think it might have something to do with using a usb connection to my modem, but Ive tried connection through Ethernet and nothing works.

Basically i just need to know how to connect my internet connection to my router, so then i can connect my router to both my laptops. I know its possible and i have all the equipment, because two days ago everything was working perfectly. The only changes i have made since everything thing was working, is that Ive reset my router and reinstalled my usb modem.
I really want this all sorted out asap, and i don't want to have to pay another £30 ($60), so if anyone could help i would be really grateful. Like i said i am really stupid with all this stuff and i shouldn't have messed with it in the first place.
I will do my best to answer any questions and give any information you need in order to help me out, and i will be logged in all day as i really want this fixed.

please help.