Seems like m-audio keystation 49e is not automatically recognized by windows 7.
The guys @maudio say that windows should automatically install the device, so they don’t provide the drivers.
Here’s the solution to install the driver:

1. connect the device
2. choose to select the driver manually
3. type in the search path “C:\Windows\winsxs”
4. install the driver

Other M-audio products (axiom etc) have the same problem; AFAIK the procedure should work even with those devices.