computer locks up with incoming phone call

We have a V92 modem on a Dell Dimension 8300 which should allow us to receive incoming phone calls while on the internet. We have gone to the Phone & Modem options and the "disable call waiting" box is not checked off. We have the NetWaiting software turned on, (the NetWaiting  logo etc. comes on when you first log on) and we have the settings for it set for "screen all incoming calls and prompt user". But whenever someone tries to call us, the screen locks up on whatever page you are on, and the NetWaiting window never comes on the screen, we are not notified we have a call and we have to manually turn off the pc and start over. We have MSN9 dial-up service and have talked to them but no solution yet. I have been testing it by calling with my cell phone while I am on the internet, but others have tried to call on the regular phone and can not get through.