First post on the forum, so please be gentle (I hope I have included enough info here).
I can generally troubleshoot (with the help of Google) some of the issues that pop up with my computer but this one has me stumped.
I am running Windows 7 Enterprise SP1 and browse the net with Firefox 4.0.1 and use Thunderbird 3.1.10 for email. When I was  running Vista then anytime someone sent me an email or a new post was written on a forum it would popup (via RSS) in my inbox. That is still happening as long as the computer hasn't been idle for a while. Under Vista it didn't matter, the emails still came in to the inbox. Now, if I haven't been on the computer for a while when I come back there are no new emails. But if I hit send/receive a whole pile come in.
Same thing seems to be happening when browsing the web. If the computer has been idle for a while and I come back to it and click on a link in Firefox (or any other browser I have tried) or open a new tab it can take 30 seconds to open the site. After that there are no speed issues browing to other sites. It is like the broadband internet connection is being dropped when idle and then it has to connect up again (when I click on a link or hit send/receive). It has done it with 2 different modem routers (initially a Belkin F5D7634 and I am now using a TP-Link W8960N). I have also talked to my ISP (Orcon) and they tell me that my connection hasn't been dropping out. Pretty sure it must be a Windows 7 thing but can't for the life of me figure it out and Google is no help.
Anyone have any suggestions? It is bugging me because the RSS feeds from the fishing forum I'm on only download 10 items at a time, so if I have been away from the computer for a while I have missed most of what has been going on as only the 10 most recent post download where as in the past everything would pop into my inbox as it was posted.
I have made sure that the power management feature of the network adapter is turned off.

(as an aside - and not sure if this is related or not - most of the emails in my gmail account have recently stopped being downloaded to Thunderbird. I get emails from Grabone each day and that is it. However, all my other emails are there in my inbox if I check online and they are downloading fine to my iPhone).