Nios 2 can't locate the USB Cable

Hello,

I made a testing system for my LCD with the SOPC builder. I was able to program and verify it as well in Eclipse. However when I started my PC today, I saw that the C program can not run, since under "Run Configurations" no cables were found. I tried to hit the "Refresh Connections" button multiple times, since it usually works. But no use.. Meanwhile I noticed that my other Nios projects also fail to execute due to the very same reason. Anybody knows what's going on? What shall I do?

Thanks in advance