Problems with external monitor not displaying

Hi,

I have a XPS  L502X  hooked up via VGA-HDMI  to my admittedly older E228WFPc. Dell monitor. I have been using this set up for the better part of a year without any real problems. Then I had to unhook the HDMI cable and when I came to reconnect today - nothing.The laptop believes it is connected but nothing shows up on the monitor. Any suggestions?

Thanks

Wondering42