My friend had an hcl laptap with windows xp professional 1 gb ram and harddisk 160gb and the video memory 256mb and every thing in new computers commonly have installed recently he said that he had gone to properties (through right clicking on the desktop) and
changed the screen are to some large amount of pixels and applied it then it hanged and from that time there is no display on the screen (even if restarted ) please help him through me i am waiting for reply

Try booting into safe mode or last known good configuration.
Maybe reinstall the video drivers.
Getting into Windows Safe Mode