Anyone has a mod list to make Fallout 3 and New Vegas to look brand new
Not possible. There are texture mods the like that update the look a bit, but there's only so much that can be done with a game that's 13 years old, short of just remaking it entirely (which fans are working on by rebuilding both games in the Fallout 4 engine, but neither one is done yet).
and maybe add a bit of randomness to the games ?
For the former, I was looking for like enemies that can have all kinds of weapons and I remember there was one for Fallout 3 that added the DLCs creatures to the main game
Project Nevada, FOOK, Fallout Wander's edition and Marts Mutant Mod all add new weapons to the game that enemies can use or new monsters and enemies.
Nevada and FWE I strongly recommend, MMM and FOOK I have reservations about. The latter two IMO add too much stuff that sticks out as being modded content, vs the others that fit into the game much better. The version of FOOK for New Vegas is much better though.
I discuss these mods and other in more detail in a post here, if you're interested.
Anyone have any idea how to fix this issue?
Perhaps try to uninstall it again and this time make sure to go into the steam opitions and delete local files?