Wi-fi router not in range

Geez! I really messed up my question.
My cell was able to connect to my wi-fi router until I tried to connect another cell. I connected the other cell but my first one shows a 'not in range' message. I now have 2 computers and one TV set connected by cable and a tablet and one of the cells. Is there a limitation to the wireless connections? Should I shop for a new, more powerful router and what do I look for? The router I now have is a D-link older model.