Restart Screen Sharing Service on Mac mini Server

I'm running Mac OS X (*think* it's Snow Leopard - 10.6.7) on a Mac mini. I'm trying to connect remotely from an iMac (this has been working fine in the past, for some time). When I click "Share Screen..." in finder on the iMac, I (eventually) see the server's desktop, but it appears to be frozen. However, I've managed to determine (from closing the window and sharing screen again, on repeat) that it IS actually receiving input, just not updating the display. I can ssh into the server, but how can I restart the screen sharing service?