LCD screen goes blank.

[#1]

I've an LCD screen on a multi screen win 7 system. that after warming up goes blank (if I cycle the power switch it stays on for a few moments, If I 'replicate' an existing screen it stays on).
I've dismantled the screen and checked the power supply and capacitors - all OK. When it goes blank, if I shine a flashlight up close to the screen, the monitor appears 'on' without any backlight. so looks like the 'backlight' has gone.
Any suggestions would be appreciated.

[#2]

The tubes over time put more of a load on the inverter which in turn will turn off if it senses an overcurrent situation.
Also don't rely on a visual check of capacitors as they don't always bulge or leak when dead .......

[#3]

I'd agree that just looking at caps is not a good way to see if they're dead, you need to physically remove them and probe them with an ESR meter to be 100% sure if they're failing, but that's getting into intermediate electronics, the symptoms you describe, assuming it's not an LED-based monitor, are either a bad inverter circuit, or the CCFL tubes are failing...
If the inverter, you could probably replace it, but if it's the CCFL tubes, unless you're really handy, then they're hard to replace being so fragile and easy to break, and would be far more cost-effective to replace the entire monitor, or if you can find one, the monitor's TFT panel, but again the replacement of the entire monitor would be more cost effective (but stick the old one on ebay as someone might like to buy it to repair or use for parts, Reduce Reuse Recycle Repair!!)...

[#4]

Quote from: DomS

Also don't rely on a visual check of capacitors as they don't always bulge or leak when dead .......

+1
If in doubt, rip them out (and then replace). I have a monitor in the shed that had 6 dodgy caps. 475uF iirc, bought a bundle box of caps from maplin which only had 5 lol. Replaced the 5 worst looking ones hoping to see some improvement and for a week it was fine.. and then started playing up again. I've not bought anymore caps as I'm too skint. The monitor still lives in its box in the shed  One day...

[#5]

Don't bother with maplin, like Radio Shack in the US of A, they no longer give a rat's posterior about the fixers and makers, they'd rather sell cheap and nasty pre-packaged tat that you can buy off dx.com for less, buy your components either from a local electronics shop (if you have any left), or online from reputable outlets (Farnell, RS Components, etc.) or via ebay, and use 105 degrees caps instead of 85 degrees, they'll last a lot longer...
I'm just sorting through some caps myself actually, preparing to re-cap a pair of Amiga A600s which recently had their onboard caps vomit their innards, I'm replacing most of them with Tantalum capacitors as they will last a lot longer than the stock electrolytics and not leave a mess on the boards if they do eventually fail...

[#6]

In the old days a blank screen was usually down to a failed inverter or a failed lamp.  These days monitors tend to use LEDs instead of the lamp so presumably no longer require an inverter.