My monitor has kicked into sleep mode and won't "wake up".
Unplug all the Cables from Compaq Presario 5103 CL and leave the Keyboard, mouse and monitor cable pluged in.
Now make sure the power cable of the monitor should be pluged in and the power cable of the tower should be pluged in.
Now to check if the montor is fine just unplug the video cable only which will show no input signal on the screen. If it shows this signal the monitor is fine. Plug back in the video cable.
If the monitor is going to sleep mode it might be possible that the old computer ( Compaq Presario 5103 CL ) is in stand by mode. hit any key on the keyboard and it should come back .
If it is not in the stand by mode then do one thing. Check the same monitor with the new computer. If it is working. Perfect ..!
Do one thing now ..!
Unplug all the cables from your old system and then press the power button for 30 sec and let it go. Now plug the keyboard, mouse and the monitor try again.
If it works Perfect. If not ..!
Then you need to open the tower and check on the processor FAN is it running..? If its not running you will not get the display as the fan is responsible for the display on the screen. Otherwise...!
Check the Tower possibly the Tower is not getting the power.
Try these steps and let me know If it works