no monitor stated, ! wow. (hard to help this)
generic PC 101:
1: test this monitor on any other PC.(vga)
2: test this PC on any other VGA monitor .
either test above quickly proves which end is bad.
easy no?, just one simple test and 1/2 the causes go byebye...
if the PC goes dead the monitor goes to sleep mode. and HP monitor shows yellow power. lamp.
I will do simple monitor tests now
even with NO PC connected. (basics)
1: most monitors will even a sign on message, with no PC.
a HP logo graphic, Compaq logo shows. or some text.
newer monitors show logo message "energystar" every time.
then shows..... (the last means PC is setup wrong)
OUT OF RANGE.
errors. then goes black.
if it shows nothing ever, the monitors 15 year old
CCLF tubes inside are now dead, 99% are now.
the LCD back light lamps died long ago , on most.
if the back lamps are good from year 2003,.wow
then.... (like finding 1995 car that runs)
the monitors OSD screen on most will work now.
on demand !by YOU.
for a few seconds, lacking a PC connection.
power on and hammer the menu key see OSD.? even for 1second.
This works best with working PC, the OSD will not work at all with a dead PC but some screens can be tricked into showing the OSD for few seconds at power on, no PC conn., (it's super good to know these facts,when screen is dead or partly)
you asked about the magic batteries. (cake walk)
well sure, all 15 year old PC have bad RTC coin cell battery on the DESK top , inside mother board.
if never serviced for 15 years it is bad.
replace it, (below 2.9vdc is bad battery(metered)
remove it look at number and get one at walfart.
2032 cells are common
(camera dept, or watches)
my nice test monitor (tech)
HP lE2000x (led) nice and small.
power on (no PC connected)
blue lamp power button glows every time it gets power.
Large menu pops UP, shows scanning VGA/DVI and more for 2 to 3 seconds
then a large white menu pops
and shows "monitor going to sleep" in clear English. (means PC is dead , this case missing)
the blue led power lamp goes from blue to yellow
and screen is now black. (all 100% normal)
these are what all LCD do powered on.
if the monitor is totally 100% dead all ways from Sunday, then it is. as all are now with CCLF tubes
99.9% are dead, if used.
the lamps last 20,000 hrs and DIE.