It sounds like one of two possibilities:
1) Your ISP is overcommitted and kicking off customers who are idle for very
long to allow for new logons. This means they aren't lying when they say
"everything is working fine". It would seem likely because if the 15 minute
2) Your dialup line has acquired some noise, possibly from water, corrosion
or proximity to AC wires. Often people may rearrange wires and leave AC
lines and phone lines running parallel, this can cause inductive noise in
the phone line and cause slow speed or signal loss.
You didn't say what OS you are running or what speed you are hitting.
If you are using the external modem you can pick them up for free from used
shops or a MUG member. An internal modem will probably run you $50 on eBay.
It would probably plug into the CommSlot pictured here:
The modem card would look like this:
Unfortunately the Global Village CS modem is scarce and costly.
Hope that answers some questions.
Entity harryted spoke thus: