|Why are you assuming it's going into Standby ?|
A computer does NOT go into Standby when you first boot it.
You should get normal video at least while booting before Windows is supposed to load. The computer doesn't need any software that's on the hard drive to produce video while booting,and resolution settings in Windows can't have anything to do with that.
If you are always getting normal video while booting then no video at all after Windows is supposed to load, that's usually easy to fix.
If you are always getting normal video while booting then after Windows is supposed to load you see only a blinking cursor, or if you see the first part of graphics for Windows then the computer Restarts, there are things you can try to fix that situation.
If you are getting no video at all, you may see a message on the screen generated by the monitor itself No Video Signal or similar, lots of things can cause that, but going into Standby when you first boot it isn't one of them.
Apparently compaq presario s5100uk is a desktop computer .
E.g. One of the most common reasons for no video at all is the power supply is failing (it partially works) or it has failed completely (no leds come on, the hard drive does not spin, fans do not spin).
Apparently, power cords for computers sold in the UK often have a fuse in the cord, probably inside the male plug. If the power supply is not working at all on the computer, check that fuse.