Good news: My delidded Core i7 3770S works. The remaining on-die thermal paste were some hard crumbles, so it wasn't a bad idea.
Before this I made a backup of my old installation, and during compressing the disk image the Core i5 was more than 100°C !
I've never seen something like this on my Ivy Bridge CPUs. As I removed the cooler, there was not much thermal paste on the Core i5.
The mainboard must have been in an preinstalled system, instead of the 'Gigabyte' BIOS logo an OEM 'Hyrican' logo is shown.
The BIOS is UEFI, but in pure text mode, no fancy graphics. But the original BIOS looked the same if I check the manual.
But it will take a while because I can rebuild it. Because I added a huge cooler, I can't insert a 3,5" HD without removing the cooler
or the mainboard. So I want to prepare a HD first, and I have to clone the 4 TB HDD from my main system. This will take some time.