does a black screen appear? if so then probably your ram memory has a problem.
can you at least see boot menu appear after restart? try to shut down your computer then turn it on then after a few seconds restart. if still black screen then next try using boot disc if it's not a memory problem you might see boot screen. if nothing happen still. then probably your ram memory has problem as well as other part in computer and cpu too might be the reason, but in most cases memory problem causes black screen when you turn your pc or laptop you can hear it's working but all you see is black screen with nothing on.