First of all, may I ask if you have a mini disc player or a Sansa Clip? Because the Sansa Clip does not play discs of any kind.
If you do indeed have a Sansa Clip you will find the FAQ rather helpful here - http://www.sansa.com/support/sansa_clip/faqs
Question 9 there is regarding devices not recognized by the PC and the solutions are as follows:
The most common reason for this problem is not having the latest
Windows Media Player installed, or having a Windows OS version that is
not supported by the Sansa player.
The Sansa players support Windows XP SP2 and Windows Vista and
above. If your operating system version is supported by the Sansa
SOLUTION 1 – Download and install the latest Windows Media Player
SOLUTION 2 – If that didn’t help, and you are running Windows Vista, apply the following hotfix - KB940199
SOLUTION 3 – If that didn’t help, download and Install the MTP Porting Kit (click here
SOLUTION 4 – If that didn’t help, try connecting the device to the PC using MSC mode
Clip: Go to Settings > USB mode & choose MSC
If none of the solutions work for you, please post the results of your attempts and we can go from there.