Black screen after installing nvidia driver

Well, for power-well support you need the i915 kernel module.
As this hangs your system, I don’t see any other way than to just ignore that message.

Ok, then I will do that. But there is no risk of damage for the hardware, isn’t it?

No, not really.

I got curious about this, it seems that the IGP is automatically switched off when the BIOS detects another GPU. Source Intel, so it should be reliable.
https://communities.intel.com/thread/42625