Desperately Need Help: Why won't remote desktop work w/VPN to a PC?

I am seriously losing my mind and the IT people at my job are clueless. I am not that sophisticated but, when it comes to macs, I might as well be a genius in comparison to them. At work I have a PC running Windows Vista. I have installed on my Mac (running Mavericks) VPN through Netextender. I can connect to VPN with no problems. However, when I try to login thru remote desktop, it tells me my work computer cannot be reached. My work computer is most certainly on and reachable. I desperately need to figure this out!! Please help!