^ Pretty much this. I'll let Vipershark handle this, but to go into a wee bit more detail your computer comes with a big board on it that's responsible for connecting you to the Internet, called your "network card". Typically, with inexpensive computers it's integrated into the motherboard, but sometimes you can find them installed in one of the PCI slots (and to add one or take one out, you pop the computer open and then insert the card's "teeth" into the right place on the motherboard and make sure it's lined up with the back and fits flush so any cables needed can plug into 'em) If for some reason your internal network card blew (which, odds are it probably hasn't; that like never happens. Don't worry) you could replace it with one of those plug-in network cards. Or, if you didn't care about gaming (judging by the Steam icon...you do) you could get a wireless network card, plug it in and use that instead!
Typically, Windows 7 comes with a plethora of drivers right out of the box and your computer should recognize them, so this typically isn't a problem. However, some companies have since added new boards that aren't immediately recognizable after a fresh install...which seems to be the problem you're experiencing atm. If your computer came with an installation disc, check those first to see if they've got the missing drivers you need, but being it's 2015 the odds of that are kind of slim.
(You probably knew all this, but uh, let's say you had to explain it to your...cat. Yeah, that's it, I just simplified it so you can better explain it to your cat who is clearly concerned about your connection issues)
Typically, Windows 7 comes with a plethora of drivers right out of the box and your computer should recognize them, so this typically isn't a problem. However, some companies have since added new boards that aren't immediately recognizable after a fresh install...which seems to be the problem you're experiencing atm. If your computer came with an installation disc, check those first to see if they've got the missing drivers you need, but being it's 2015 the odds of that are kind of slim.
(You probably knew all this, but uh, let's say you had to explain it to your...cat. Yeah, that's it, I just simplified it so you can better explain it to your cat who is clearly concerned about your connection issues)