I am having this problem on two machines as well. Both are as follows:
1. Dell Precision M4600 with Ubuntu 12.04 (fresh build within 30 days)
2. Dell Precision T1650 with Ubuntu 12.04 (fresh build last week)
I am using NVidia drivers at the moment, and will deactivate them for now, as my symptoms are exactly as described.
I am having this problem on two machines as well. Both are as follows:
1. Dell Precision M4600 with Ubuntu 12.04 (fresh build within 30 days)
2. Dell Precision T1650 with Ubuntu 12.04 (fresh build last week)
I am using NVidia drivers at the moment, and will deactivate them for now, as my symptoms are exactly as described.