DSL Connection Problem

I am having a problem with my DSL connection. After about an hour or so, no addresses will resolve any longer. The connection still works, but only with straight IP addresses. I can still ping my DNS servers and get a reply . WinIPcfg shows that the DNS servers are active. This problem only started occurring after I reinstalled windows after I got a virus that messed up my system. I also had to reinstall my DSL modem software. I have used System File Checker (SFC) to check for messed up system files. I have installed every possible update there is. Still does the same thing. Disconnecting and reconnecting doesn't solve the problem. I have to restart windows to get it to work again. Does anyone have any clue what could be causing this problem and how to fix it? Having to reboot every hour or so is extremely annoying. I have an AMD Athlon 1.4GHz/512 MB RAM/3COM internal PCI DSL modem and Bellsouth FastAccess DSL service.