Wireless Network Connection

Hi all,

Have a very frustrating problem. Have a HP Pavilion Elite HPE desktop PC running Windows 7. I recently changed my router/modem back to my old Belkin N. The computer has connected to it in the past. For some reason it will refuse to connect wirelessly now. When I put in the security key is tells me its incorrect when I know its 100% right and when I use the security PIN off the modem itself it will just say its unable to connect. My Laptop, ipad, xbox, samsung galaxy 3 etc all connect fine. I have done the following to try and rectify the problem

-Installed the wireless profile from my laptop to the HP via USB
-Uninstalled and reinstalled the wireless network software
-Done a factory reset of modem/router
-Removed all wireless device profiles from the PC
-Created a Manual wireless network profile

I am now coming to you guys for advice. Any help will be much appreciated.

On a side note the PC was previously connected to a Netgear N600 wireless modem/router.

Thanks