Tablets lose connection when assigned static IP

I have a mix of tablets, different brands/models, with the same issue on each one. The majority of the tablets are HP Slate21's.
I have a Windows network/domain, and wifi access points around the building connected to it. My tablets fully connect to the wifi (able to access both intranet and internet sites) when set to DHCP, but when I assign them a static IP, they drop connectivity. The wifi actually still shows as being connected, but not active, no access to either intranet or internet.
I'm assigning them open IP's so there is no conflict there.
I've tried the IP of the wifi router as the "Gateway", as well as our actual domain gateway, and including/not including DNS 1 and DNS 2... any combination of settings I could think of, all with the same result.
As soon as I reset them to DHCP, it picks the connection right back up.
If anyone can give me any insight as to how I get this working, I'd really appreciate it. Thanks.

 

Thanks, I appreciate the replies.
If it's a router issue, I can take care of that. I thought just setting the IP on the tablet would be enough, was thinking it worked like it does on a pc. Thanks!

 

I figured it out. I had the network plugged into the WAN port on the router, which I'd also set the IP for. Just had to switch the plug to a LAN port, reset the IP on the LAN setting, and the tablets took the IP's.
I spend so much time with this stuff, sometimes I can't see the forest from the trees. I appreciate all the help, sometimes it takes bouncing the problem off someone else to shake it loose in my own head. Thanks again!