Do you remember your login info? Your library is saved on your account. You may have deleted all your games from your PC but you still own them. Your friends would appear on your account as well unless you went through and unfriended each person. Screenshots might be an issue. Not sure if Steam automatically uploads them to Steam Cloud so if they were only saved on your PC then they may be gone if they were in your main Steam install folder. If not, your screenshots will be on your account as well.