Console port doesn’t work on Catalyst 3548XL

Hi
I’m studdying toward CCNA Cert and I just bought catalyst 3548XL on ebay. Workd fine when I first time boot it up, but for some reasons I can’t connect to the switch now. I get a “Unable to open COM1.Please check your port settings”.
Now! I know i look obvious but in fact all setting are fine I’ve got 6 other routers plus a 1900 switch and I don’t have any problems with them.
Last time I was using 3548 was when I was practising OSPF and I didn’t do any configuration changes.
Thnx for any answers
Dariusz