Ok so i brought my computer home after a 2 week stay at my brothers house.I then plug everything in and started my computer and my screen up.Now the problem is when i turn on the screen it says"monitor in power safe mode,activate by PC".How do i fix this?

Move the mouse or press a key?

Make sure the monitor cable is correctly attached to the gfx output, and that the graphics card is still correctly seated in the VGA/PCI/PCIe slot.

i moved the mouse and pressed the key and nothin happens.its still in the slot and ive tried many times but it just doesnt seem to activate

Looks like your monitor isnt getting input.
Check the cables, and try windows safe mode...

Quote from riffey4 :

Check the cables, and try windows safe mode...

If the display from the BIOS doesn't work, then what makes you think safe mode will?

ok i got my monitor to work again thanx.But theres one more problem.Whenever i play LFS the screen is fine but sometimes it flickers.Its like the snow from ur TV when u dont have signal.How can i fix this?

In case you didn't solve your problem yet try moving the VGA cable away from electrical noise sources (power cords, electrical appliances cables, calculators, magnets and especially speakers and cellphones).

I'll add a general hint, when you solve a problem tell what the fix was, it may be helpful for other people having the same issues, and to solve further ones.