The client is probubly running hidden. To check if the client is running you can use system monitor or even better you can use Microsofts' Win Top and a log file (enable the logging at the cliets configuration). To access the configuration run
Just an idea, Micron... could you be clicking on the icon for the Dnet screen-saver (blank screen)? I've done that plenty of times so I thought of it first. Maybe you moved the folder that the icon points at otherwise? When in doubt, you can locate dnetc.exe manually and make yourself a fresh shortcut. If dnetc.exe won't run when you click on it directly, you may have to reinstall the client. Let us know how it goes... : )
Hey, just thought of another possibility. If your client is set up to do only OGR, it will not run if you don't have any OGR work units left in your buff-in.ogr, since it cannot do a random OGR work unit. You can tell if this is the case because the size of the buff-in.ogr file will be 8 bytes if it's empty. If that's the case, try connecting to the Internet and then starting the client, in which case it will spot the connection and download some fresh work units.