USB connection

Hi,
I have a now strange phenomena with the Repetier program.
I use Repetier 1.0.6 and Repetier 1.6.2 with the same result.
When I press Connect, it connects , and if I load, slice and print a model nothing happens.
The temperature of extruder 1 is 0C and extruder 2 is 100C.
If I pull out the USB plug, Repetier stays connected.
the PC notices that the USB is disconnected, beeps.
I have tried several USB cables.
It worked always until this week.
I even bought a new Mainboard with no results.
HELP

The problem is with the temp of the hotends.
0C will cause a min temp error
Check the resistance of the thermistors (unplugged)
At room temp they should be around 100K

Hi, thank you.

It is not the problem .
If so, then you see a Mintemp Error in the display, and that is not the case in my case.
I can still print from the SD memorycard. That means that printer is OK.
I think that it has to do with the USB connection or with the settings in the repetier program.

Is something wrong displayed in the log window in Repetier?