LeylaLou

Hi there, I was wondering if anyone had any ideas on how to solve my problem. i bought a new desktop today from PC world, when I got home and set it up the monitor comes on very briefy and then a message pops up saying its going to sleep and it turns itself back off and I can't get it on. I managed to set up the computer using an old monitor (of the pc I am using now). I know that the computer is speaking to the monitor as when I turn the monitor on and off it very briefly shows me the screen and I can see that it has loaded windows etc I have tried everything that it states on the HP support site but to no avail, and I can't seem to even access the menu by pressing the button on the front of the monitor. Do you think I have been sold faulty goods? or is this something simple that someone with much more know how than me is going to know how to fix. Any help would be greatly appreciated ... but please remember I am not pc savvy so an idiots guide would be good! Thanks :(