unable to boot RHEL 7 after installation

Quite weird from my perspective.
I joined the developer program yesterday, downloaded the iso-image and installed it on my Intel Nuc (Celeron N2820, 2,4GHz, latest firmware) with 4 GB RAM and a 128 GB Samsung 840 Pro SSD. Server listens to DHCP but with a fixed IP address configured in the router.
I made three attempts:

1st:
UEFI and Legacy boot with UEFI as preference.
Installation (minimal) successful without errors. After booting the new system I ended up on a black screen with two penguins on the top left corner. Nothing happened after that.

2nd:
UEFI disabled, Legacy only.
TSC problem upon starting the installation DVD.

3rd
UEFI enabled, Legacy disabled.
This time server installation with GUI, again no errors.
Upon boot, you guess it, the two penguins at the top left corner of a black screen.
Booting in 0-rescue started up the GUI with the Red Hat registration process. Restarted - same result. Restarted again in rescue mode took me to a grey screen - nothing happens. At least I can ssh from my Mac into the server and I could return to a tty with ctrl-alt-F1 (or F2). Installed all updates.

Actually, I would like to normally boot into my RHEL. After having spent around 6 hours now any help is highly appreciated.