I recently decided to switch distros on my main computer, so I backed up my files and did a complete clean reinstall of Linux Mint on my ex-Arch machine. I had one partition, which is the default Mint install. After rebooting the first time, everything was fine. The second time, grub's interface did not appear, there was only a blinking cursor. I booted the liveCD, reinstalled grub, no repair. I then reinstalled Mint all over again, same problem...
What am I doing wrong? I never had this issue and the livecd is not corrupted, I've already used it to install Mint on another machine...
I must point out as well that the second time I installed it, my firs poweroff was a forced shutdown.

How new was your Arch installation? If it is more than a few months old it probably used legacy grub and that doesn't play at all well with the grub2 that Mint uses. If there is something of that left over from your backup, it could be a source of trouble.

There are various boot repair disks (Super Grub Disk, Super Grub2) that often clean up such messes, and the old reliable PartedMagic might at least let you mount what's on your drive to see what's wrong.

Did you install Mint to the partition on which you had Arch?
Is Mint now the only OS you have?
How did you try to reinstall Grub? There are a number of different methods. What was the output when you reinstalled?
When you did the Mint installation, did you reboot after you saw a window pop up indicating the installation completed?

oh god, I feel dumb right now... The grub and everything was fine, I had forgotten to take out my USB stick, on which I have an unfinished Linux From Scratch distro, and my BIOS is set to boot in the usb first...
As for your questions, it was a clean install, meaning I wiped the whole drive clean. So there were no traces of my old OS.
Thanks for your time anyway