Find out what your preferred and alternate dns numbers [your broadband provider can tell you but there are other ways] are and put them in the relevant box in your connection details [first, select the 'use the following dns server addresses' option.] if you're on xp, to get there go to start, hover over 'connect to', right click on 'network connectiions' , left click 'properties', then scroll down the list that is in the 'general' option; highlight the last item and click the properties button below it. Don't fill in any IP addresses. Fill in the DNS ones. that solved my recent wonky connection.
If that doesn't solve your problem, or even b4 trying that, switch your router off for a few minutes. Routers get gunked up from noise on the line. and/or run an antispyware program. and make sure all phone connections in your house/flat have a dongle thing stuck in them to dampen noise on the line. also, zap your temporary internet files. and make sure you are getting a strong signal.
also, note that wireless phones systems can effect wireless broadband signals, as indeed can neighbours' wireless broadband signals - you can get into your router and change the network number you are on, and see if that improves things, just in case your neighbours signal is upsetting yours.