or monitor will not turn on... all that happens is every 10 seconds or so a white flash happens.. the green light is on to indicate it is turned on...... is it knackered???
If it's the latter, I'd look at the power-capacitors on the PSU board inside the monitor - likely that you've 'popped' one (or more).
Fix = 'about' £0.80, if you know what you're doing.