Hi! May be someone here could help me!
Everything was working fine until one day I tried to connect to my RB750GL and it’s not letting me in.
I tried Winbox, Webfig, SSH bun no success.
Since the last time I connected to this router there were no changes in the routers configuration.
I’v got a backup of this router, but its made by our ex-coworker and I don’t know if it is complete, so I’m afraid to reset the router.
Any ideas?
Reset the router, put backup there and check if it is fine… If not, reset to blank config and set it freshly.
And then, once you have it correct, BACK IT UP!
Personally, my two RB750 routers create a backup and export file every night and E-Mail those to me. I don’t care if it has not changed in months - I have a backup and export less than 24 hours old. Done with a script I found on the wiki and adjusted for my purposes.
That’s what I do also. But having the export is much more useful when router dies and you need to put there some other device. In this case the backup is for nothing.
Yeah.. that’s not realy helpfull. 
sounds like you locked yourself with a filter rule. If so, you only real choice is a hard reset.
Personally, I have a server that names an SSH connection and runs an export - which is captured and saved in an SVN repository. This gets me a backup every 6 hours, and doesn’t have to write anything to NAND. And SVN lets me see what changes happened and when.
You’ve probably tried, but …
Have you tried to log in with winbox, plugged directly into the router (or otherwise trasnparently bridged to the router), by MAC address? Older versions of winbox allowed this, can’t seem to find out how on mewer versions, so I keep v2.2.18 in my laptop just in case … Just the other day I locked myself and 100+clients out with a misplaced filter rule, and I wasn’t in safe mode … I was over an hour’s drive away from the router, but could still connect to a distant wireless AP … so I just changed all APs and routers in between me an the target router to bridges, and was able to bounce in using mac address on winbox. Worth a try if you haven’t tried yet…
There was situations where ros forgot the password by nand error or so. Trying the login defaults may get you in. Maybe your device was poorly secured and someone changed the login credentials. Trying mac telnet from neighbouring device may help too if there is firewall problem.