Some time ago I made my own „OS” based on mint(Debian Based distro). About u week ago I deleted 3rd partition with Ubuntu. Before this weekend I got BSOD on windows, so I'm stuck on mint. And here is my problem with third OS: i deleted accidentally grub. The problem is yet bigger because filesystem was btrfs. I copied all files (even system)to external drive and formatted partition with mint to ext4, then I recopied system and tried with GRUBrepair. As I saw root and sudo was locked (mint doesn’t have su by default), so I tried to repair by myself. Now system is stuck between: grub shell, busybox shell (initramfs error), live boot mint and „shell”with prompt for root password (i didnt setted up that YET). Is there a way to boot PC normally? Or i’m stuck on live-boot? I don’t have space for installing third OS (space which stayed after deleting ubuntu was joined to windows) and my PC is yet on guarantee... (yet worse but guarantee is only for physical things, OOF)
PS: bios on my pc is „aptio setup utility”, there is no way to disable uefi and i can’t: boot rescueCD from pendrive and/or boot pc from external HDD. I don’t have external CD/DVD reader.
Thanks for answer (if any)
Here are all commands in busybox i can use : 
Actually I didn't have fsck. So, after lot of tries I found reiserfsck instead of fsck I don't know how to run for checking partitions. So, I added a picture of it :
When I tried reiserfsck --check /dev/sda6 I got some error :
Now i have another errrrrrrorrrr, I'm stuck on screen which asks me for password of non-existing user :
Some time ago I made my own „OSWhile this is very tough. And, none of us know how you did this. So, your question might become more harder for us more than you think. I just can help you by saying try to install grub loader the possible way you can. For me, grub-loader is my "heart" whenever I lost it I just live with frustration, "tension" and lifeless that's why I always care of grub-loader. Keep trying to fix it. – Apr 25 '21 at 14:13busybox shell (initramfs error)I had created a question oninitramfs error– Apr 25 '21 at 14:13sudo fsckI don't think that it will work either.. Read it also – Apr 25 '21 at 15:01fsckwithsu.suused for Superuser(to become Root User). Read the answer. I am looking for an answer for you while this is very hard to say..! – Apr 25 '21 at 15:42su. Then, run those commandln -s /usr/bin/ntfsfix /sbin/fsck.ntfsand ``ln -s /usr/bin/ntfsfix /sbin/fsck.ntfs-3g` – Apr 25 '21 at 15:49