Windows Malfunction

I have a win Xp machine that has been acting more than a little snakey lately. Both video and modem problems as well as not being able to downlaod patches to XP. Well the patching problem went away and I replaced my videon card so those problems are gone but problems with my mouse and outlook express made my neighbor suggested I reinstall my operating system. Bad move. Now My modem refuses to configure for use with other programs such as ATT worldnet services and faxing. It is a Broadxent DSI V.92 PCI DI3631 modem with the latest and greatest drivers installed. And I get the message”rundll32.exe-Entry Point Not Found” whenever I try to look at any of the properties of my computer. Anyone have any suggestions? I’m at a total loss as to what to do now.