Belkin Wireless-N Router...Settings Help!!?

I recently bought a wireless-n Router...mode: F5D8236-4v1(01) firmware: Firmware Version 1.00.02 (Jul 31 2008 22:32:30). For some reason when i installed it, it only lets me connect to the internet when my linkspeed/duplex is at 10mbps half or full duplex. and when i have it at 100mbps half or full duplex it either doesnt connect or my internet connection would be really slow. But when my internet it directly connected to my PC..i am able to run it at 100mbps half/full duplex. Does anyone know why my router wont run at 100mbps?? because i lose a lot of download speed. for example i tested this one file where i download at 1.2mb/s when theres no router connected but when there is i download at 500kb/s. if anyone knows the reason why tihs is happening it would be greatly appreciated. Please and Thank you.