The HP L2045w has a resolution of 1680x1050 according to the specifications. Which means the following added to the bottom of your
/boot/config.txt may send it the right signal (although the VGA adapter can add a spanner in the works):
It looks like it has a DVI-D connector in the back, too, under certain circumstances it’s possible to get an HDMI->DVI cable or adapter that will fit that port.
Here’s the adaptor we sell: https://shop.pimoroni.com/products/hdmi-to-dvi-adaptor
Do you see a port on the back of your monitor that would fit this adapter? Pay careful attention to the pins, it should look at least like this- with the little slot on one end:
If all else fails with the VGA adapter, then I believe this should work as long as the port in the monitor has that slot, ie: is keyed for the adapter.