If you have a monster KDR you will play with monster KDR's ( Mostly Hackers )
If you have been flagged by VAC/IW for a delayed ban on next update, You will only be able to play with people in the same status.
Solution : Trainer to lower your KDR,
Solution 2 : Delete config_mp.cfg, And do a check for missing files with a friend's non-flagged account.
PS : Solution 2 won't save your ass from a delayed ban, But at least you will be able to play until your ban =P
Solution 3 : Don't get detected / don't get hacked monster stats you morons.