my computer and monitor are on but the screen does not show anything (black), so what can i do to fix it.Are the VGA or HDMI connections at the back of the computer and the back of the monitor correct / tight?

What happens when you first turn on the computer and monitor?  Any displays at all?no any display and it is still black Any screen at all on boot ? ?tumsime rajab, 1st order of business is welcome to the CH forums. In order to make your time here with us as fruitful and rewarding as possible i would like to enlighten you as to some proper forum PROTOCOL (not only this ONE but all forums). Posting your topic as "Hi" may be an acceptable way of introducing yourself on a social forum but on the CH you will be RESPONDED to more readily and with more potential benefit if you state the real issue that you want us to help you with. As an example from your own post" screen does not show anything (black)" would have helped us to know what your issue is that you want help with. Then when it comes to actual help being forthcoming the post Allan has made in the thread of your post should become your habit when you desire our help. Hope that this advice to you will lead to a more fruitful mutual involvement of yourself as a new member and those of us here on CH that DEVOTE our efforts to trying to help you and others. For your guidance,truenorthDo you have another computer on which you can see if this monitor works?

When you turn on the monitor by itself, do you get any kind of display, such as "No Signal"?

Alan and True have good points here.  We will certainly try to help you, but try to provide us with what information you can.yes, nothing on the screen at all, so what else can i do
When you turn it on, does the computer appear to be booting at all? For example, is there a POST beep? Are the fans spinning? Is there any drive activity? Does it make a sound as if booting into Windows?

What brand and type of monitor is it? Does the monitor say anything on it such as "No signal" or "Check cable"? Is the monitor status light on? What color is the monitor status light? Does the monitor appear to be powered on at all? Have you checked that both the power and signal cables are securely connect?

Have you recently made any hardware CHANGES in the computer?

Keep in mind that we cannot see the computer. Simply asking "what can I do" without providing information prevents us from rendering any kind of help. Give as much detail as you can: computer specs, sounds, behavior, lights, smells, etc. Only then can we do anything for you.