Older computer cannot locate certificate when trying to access my home network

[#1]

I recently upgraded to the new quantum router and was able to get all my computers, tablets etc to connect. But my oldest computer that still runs Windows XP. when i try to connect it says unable to find certificate. the computer has a belkin USB adapter (N150)  that connected fine on the older fios router, but not this one...

[#2]

A certificate shouldn't need to be required to connect to the new router. Was your old router using WEP security by chance? Also, does your Windows XP Computer have Service Pack 3 installed?

[#3]

Most Cert errors are due to wrong date and time on machine. Make sure the date and time is correct on the computer

[#4]

the computer only has SP2, i believe i had WPA2