Problem with nividia drivers

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http://askubuntu.com – I am running Ubuntu 12.04 on a hp workstation Z820 (with NVIDIA NVS 510 2GB graphic card), I use a display port for the screen. The system works fine generally but if the screen is off for a while and I want to turn it on, then it goes black / gets disturbed some times. I also tried a DVI-D cable with a mini port adapter then resolution is too low. I guess some thing is wrong with Graphic card drivers but do not know how to fix it. Could any one help me with this issue? I appreciate a lot! /Omid (HowTos)