VGA splitter to monitor and tv

Our old computer finally died and I had to buy a new one. We had a VGA splitter (Y) cable connected to the last computer. We could use the monitor and our TV. We had no problems. I connected it to the new computer and it doesn't work correctly. The computer monitor will blink to black and then back on every minute or so. I have tried to change the resolution and Hz and nothing seems to work. Anbody got a suggestion?