Since the monitor stays on in safemode, this sounds more like a video card issue. Did you recently change the video card driver?

I changed the video card a year ago,Have not updated driver recently.

* Switch the monitor and PC off
* Unplug the power cord from the back of the PC
* Disconnect the monitor from the video card
* Remove the PC case cover
* Remove and reseat the video card in the motherboard slot
* Close the case cover
* Reconnect the monitor to the video card
* Reconnect the PC power cord
* Power on the monitor and then the PC
* The operating system should reinitialize the video card and load the driver. What happens?

It booted to the start menu then after several minutes the screen went black

Sure sounds like a defective video card.

I have a Dell XPS 1530 and also started getting black screens - it does NOT happen when running off battery, only when power cord is plugged in. When the power cord is plugged in it happens both in safe and normal mode. 

Interestingly, I have accidentally figured out that EVEN with the power cord plugged in and the screen black, things still work, it is ONLY the screen that blacks out.... and if you close the lid for 3 seconds and reopen it (even with power cord plugged in), your screen is visible again for some seconds to a minute or so before it blacks out again - this may help you back up data (even with the black screen, data copies just fine for hours in the background). It is interesting to me that closing and reopening the lid should "reset" whatever it is that is going wrong with the screen and may hold a clue for us.

Anyway, I also replaced my battery with a new one about 4-5 months ago, so that could also be a clue.

My business, income, livelihood relies totally on my laptop and connectivity so if anyone can help us resolve this, it will save me a packet in rushing out to buy another high-end machine for something that my gut tells me is something simple to fix.