GPU clocks stuck at minimum after system reboot

Hello,

I've encountered a weird problem with my nvidia nvs 4200m GPU on my latitude E6420: it's clock speeds are stuck at gpu clock = 270MHz memory clock = 540 MHz and Shader clock = 405 MHz no matter how much I stress it.

I've tried to do some troubleshooting. Here's what I've found so far: I've tried several versions of drivers. After driver installation and before first system reboot after that installation GPU is able to reach the clock speeds I've configured in nVidia control pane under performance tab. However, once I reboot the system nvs 4200m stucks in the minimum clock speeds. 

However, I've been able to find one remedy which isn't quite optimal though. If I disable and then re-enable NVS in Device manager graphics chip starts clocking normally.

Furthermore, the chip has severe heat problems when clocking normally (100C at any usage, slight downclocking won't help). I'm going to try replacing GPU thermal pad with a copper shim and see if that helps. That's different story, though. At minimum clocks the temeperature slowly rises to about 70 degrees celcius and stays there. Note that it doesn't throttle at 70C, clock speed would never exceed 270/540/405MHz.

Any idea how to fix this?