The symptom is an unstable IRC connection-- the underlying cause can be a multitude of things, all of which containing the phrase "unstable":
- unstable ISP route; this would usually clear up in a day/week, but you should call your ISP to see if they've had any outages/issues recently
- unstable modem; this would cause issues outside mIRC as well, but might be harder to diagnose unless you have other persistent connections. The symptom here would be that the modem dies every few days or so, though it could also just be packet loss.
- you say you have no router, but are you sure your modem isn't an integrated router? if so, see "unstable modem"
- bad connection line; if you're on DSL, this is not uncommon. I know a few people, myself included, who have had to call up their ISPs to get the line fixed/cleaned/whatever it is they do. Been a while since I've had a DSL connection, but as I recall, noise buildup due to corrosion in the line is a real issue.
- could just be a temporal network issue with the IRC server. trying another server or network would confirm it, in this case.
