How do I reset paswrd for DL524 router so my laptop can connect

I had this dlink DI-524 for about two years. I moved in with a roomate and we used it to connect to both of our pcs. We were having trouble with the router always knocking us off the internet and we would have to reset the router to connect back. My roomate finally broke down and called tech support and they set a password for the router and we didn't have any problems with it after that. When she moved out I kept it and used it for my new roomate's pc and mine. This was about 6 months ago. About a month ago my roomate bought a laptop. I was able to connect the laptop to our internet connection and it worked fine until today when none of the computers could connect. I followed the diagnostic instructions of my computer saying to turn the router off and on and to do this i reset the router. it connected back to the internet for both of the pcs but it wont for the laptop. When I try to connect the laptop it says that it is not receiving a signal from the wireless router. The router is now out of warranty and they are trying to charge me thirty something dollars for tech support! so I'm trying to find the solution on my own help!