I have a Linksys E1000 running on the latest firmware available from the Cisco website. When my main PC (Windows 7 64Bit SP1) which is connected with a ethernet cable is running the wireless speed is great for all my connected devices. (Android/Apple phones, tablets, family PC, etc). But when I shut down my main PC the wireless speed drops to the point where it can take 3-5 mins for google.com to load up. The wireless connection is still showing as strong, just the speed isn't there anymore. If I were to turn my PC back on, everything will load up almost instantly and be back to normal. I've tried reinstalling the router, resetting it all back to default settings and re configuring it but I've had no luck in solving this. I've come to a dead end at trying to solve this, and thus I've come here in hopes someone has had a similar issue before and might know how to solve it.
It almost sounds like your PC was configured as a proxy, or some sort of caching service. So when the PC is down, all the other devices lose access to it and perhaps timeout waiting for a response. Was this PC recently used in some other type of configuration? Maybe running ICS? Maybe as a DNS server and the other devices are hardcoded to use it?
I'm grasping at straws because it's definitely an odd situation, not something I've seen before. But those are the kinds of things that immediately come to mind. Somehow those other devices have a dependency on the PC that remains even when the PC is shutdown.
I never had it setup any other way then how it is now. I've never used a proxy, or setup a DNS server (all my DNS settings are set to auto). And the only device running ICS is my tablet. The only thing I can remotely think of is I installed a SSD a few months back and did a fresh install of Windows on it, but I'm fairly positive it was working fine after this and don't see how that could of caused this.