Dalite is right, if it is a PS/2 mouse there shouldn't be conflicts with the modem, but it actually uses IRQ 12, 13 is the math coprocessor. PS/2 mice won't use a Com port. IRQs can and will be shared by devices that aren't used alot. What OS are you running? if it Windows 98, God help you - just kidding (sort of). Is it anywhere you go on the internet or is it confined to forums like this one and chat rooms? Also, like Dalite says, check Device Manager - look for yellow ? marks (unknown device) or yellow ! marks which will mean conflicting devices.
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