Start pc in safe mode by tapping f8 upon boot up then chose last known configuration that worked.

open your cpu remove cmos battery wait for 5 minutes reinsert it and start hope it works

If u can see the bios screen then follow what said above... If its not even entering the bios POST screen i.e showing nothing at all, then there's a problem in the graphics driver of the motherboad or your gpu (if you're using any)... Check and reconnect all the connectors and try again....

i cant go on safe mode or anything cos the monitor is not coming on lol, the pc just powers up and thats it

and no lights on keyboard either

Ok take out the video card then reinsert. Also clean dust frm fan ect while ur at it then power up if the moniter comes on click menu on the moniter and select default resoloution setting mine had same fault last week i just took out the video card graphics card nd reinserted and all was fine does it say no vga signal imput ?

just took it out n cleand it, put it back in and nowt differnt, if i press power button on monitor it says no input signal then just goes to stanby again

my guess is the cpu is dead

Surely, there's a connection problem somewhere on or inside the motherboard or ps... As the keyboard light is also not responding, its possibly some voltage lines are not connected properly from ps to motherboard... Check out all again if there's any lose and if possible, use a multimeter to check the volts

A lot of things might cause that.first, check the memory in another working pc to kno if its good,then,cpu,and then check other components on the motherboard on a working system to pinpoint which one failed or is failing, any of the above can coz no signal.best of luck