the game runs normally but when i approach the area surrounding agatha's house and meresti trainyard the game freezes. The weird thing is that i was in meresti trainyard at an earlier moment (10 hours game time, a week real time) and the game was running fine a that moment. Any explanation woud be appreciated

Do you have the unofficial FO3 patch installed? It can fix some of the freezing problems, including this one

Do you have any mods? (As this is often a source of issues when put together poorly etc).

If not and this is the default game, it could just be one of the many bugs still in the default game (even GOTY versions).

Try saving just before you get near the area, if you can find an internal space (like a building or under-ground entrance etc) and save in that first, then try and enter the area from that save point.

And as MasterW mentioned, the Updated Unofficial FO3 Patch is often a good idea:

https://www.nexusmods.com/fallout3/mods/19122

FWE mod?

I never had this problem with GOG's GOTY version, nor did I apply any unofficial patch nor any anti-crash either. And the GOG version already comes LAA (i.e. 4GB pre-patched). That's not to say it didn't occasionally lock-up/crash, notably around fast-travel or it's auto-save. Disabling auto-saves on travel helped. Waiting at least 10 seconds between two fast-travels and waiting several seconds between fast-arriving somewhere and entering a place helped. Otherwise it's likely a mod bug or conflict - and I say that because that whole region is a hotbed for spawns, and maybe you've reached a new level where a listed spawn type causes an issue. Marts Mutant Mod maybe? - that one can cause plenty of issues/conflicts. If you've added a bunch of mods try uninstalling firstly anything that affects potential enemies and their spawns, creature mods, armour mods, weapon mods. The FWE and EVE mods can also have particular issues with other mods.