Quickly eyeball the slot to see if any stuff blocks your way. Then unscrew the two expansion plates right in front of your way to the slot. Unhitch the lock on the slot. Make sure that the little plastic extension in the slot fits the small pit on the card, usually oriented fans down. Start to push in, making sure that you got the metal expansion part in rails with the gap on the back of the case. When it lodges in, push until you hear the clicking sound. Requires more force than you think, don't be too afraid on that.