I remember I used to play this game on one of not-so-old computers, kinda like in the 2000's and I think on XP. It was about robots, where you could buy robots according to your $, you had to do missions where you received money after you finished them, and after that you could buy better ones, with more $. It was pretty much 2D and simple, nothing too complicated there.
The robots where working in teams (3,4, 5) and you had to maneuver them kinda like in a strategy game, although you could've just selected one and finish the mission with it
The robots's fire weapon was pretty simple, primary and secondary weapon.
Any suggestion is more than welcomed :)

one of these . . . =)

My first thought was mechcommander until I saw 2d (though I have noticed that a lot of people seem to think thats interchangeable with "top down")

i remember "metalizer" from that time. though that wasnt as simple you describe the game.
edit: correct name

it's even a rough description of syndicate if you allow isometric view

It could still be Battletech: Crescent Hawks' Inception or Crescent Hawks' Revenge. I forget which of the two, but one of them definitely fits the description. (Most people probably don't know about them because they predated even MechWarrior 1.)

I thought the battletech RPGs only focussed on one character & mech

thank you all, very helpful, as always :D

OMG, I was looking for this title a number of years back. I remember playing this way back in the day, confused the heck out of me back then.
The tile is: Battletech: The Crescent Hawk's Inception
Here is an information site: http://www.djgallagher.com/games/pc/battletech/gamedetails.php
Has a download for the game on site as well.

Is it legal?

actually I was wrong, that wasn't the game at all. The one you recommended is way to complicated when compared with the one I'm looking for.
Mine had just mindless shooting, first and secondary weapon, and I'm starting to think it wasn't robots who were the main characters, they were humans dressed with robot suits that were really ..classy :D
Anything else comes in mind?
it could've been 3D as well, but it was a pretty "primitive" 3D graphic, more centered around the maps where you were supposed to find and shoot others who had robot suits on

No. The only freeware MechWarrior game is MechWarrior 4: Mercenaries--everything else isn't legally distributable; this includes MechCommander 2--the free release is source-only and lacks assets, so any download of the game in a playable state is actually warez.