can't connect to internet

I just  restarted my optiplex gx260, and i think i may have accidentlally deleted some program files. i can't connect to the internet, and my monitor is not being recognized when i go into device manager it tells me that my ethernet controller, multimedia audio controller,, and video controller are not installed (code 28). can someone tell me what to do or what files or drivers are missing? and yes i am as close to tech illiterate as you can get, so please keep it simple

Thanks alot in advance