One other thought comes to mind - you could have some other device that's causing network issues. I had a Maxtor network-based backup drive (horrible, horrible product) that would occasionally crash and become unresponsive. The problem is, when it crashed it would sometimes take down the entire network with it - it seems it was randomly flooding SOMETHING that would cause all other traffic to slow to a crawl.
I also had a PC crash once taking out the network - I was on my laptop surfing, and suddenly everything died. Rebooted the access point, nothing. Got on my desktop and everything was dead there too. Couldn't get to the internet, couldn't access the router's page, couldn't access any other PC. Rebooted the router, cable modem, switch... nada.
Eventually I just started disconnecting everything from the switch, and it turns out that one line in particular was the problem. Connected and nothing would work, disconnected and everything was fine. I went over to the PC hooked up to that line, and it turns out it had locked up. Rebooted it and suddenly all was fine.
Just some more food for thought!
Typically I just set static devices on the network out of the pooling range of the router and call it good.
Hopefully you're doing these static assignments through the router itself?
