Acer travelmate 2420 will not connect on dialup

Just received a laptop from a friend and I only have dial up and i can here a dial tone but receive error message 678. I tried to install my own antivirus also but another (pc-illian) is blocking it and that program is not in the add and remove programs and I can not find it to remove it. I thought maybe it has a virus. It has XP sp2 installed and it states the modem is working properly. I have tried everything I could find on the net to fix this problem. I'm not an expert on pc's but trying Is the modem fried?