The As500 is not the monitor's model #. You need to look further. The problem you decribe indicates a power problem inside of the monitor. List the model and what info you are looking for

okay, the model number is E152FPc...and the monitor once turned on, will go into what looks like a muted sleep mode what's on the monitor is still there, but suddenly very very dark.

You have a several year old 15" lcd. Is it worth putting $100 into? If you can do electronics repair, you can get a board for less and do it yourself. If you can do component repair, you can fix it for less than $30. The cost is in labor. Just like painting your house, the paint cost is small compared to the total. I have not yet fixed a "c" model so I don't have much guidance.
If you are capable and wiliing, you can tackle it yourself. If not a dead monitor that has not been attempted repair is worth something to people like myself who have the background to repair these things.

thanks!