Do you get the red X thing or did it only partially disconnect. If you do IPCONFIG /all does is say disconnected or does it just not have proper IP information.
If it is actually disconnecting it is likely a bad cable. Even cables from the very best companies can be defective. All it takes is for one end to be just slightly loose internally and as it get warm it will move internally and disconnect. If you bought "fake" cable it is have even more problem especially on longer runs. Make sure you have cat5e cable or better if it is cheaper. You want pure copper wire (no CCA) and it must be wire size 22-24 (no flat or thin wire) In many cases like yours people buy that flat cable because they feel they can hide it...