Mostly blank screens with moving streaks of light

Can you check that you haven't moved the little toggle switch on the side of the 4-way controller/wheel to the L (or Lock) position? If it's locked then you won't be able to move the focus field in the viewfinder.

Have you tried using a different lens ?

The most likely cause for this is a damaged or defective flexible ribbon cable that connects the vewfinder LCD to the camera body and can be repaired fairly inexpensively. However, it's not a user serviceable problem and will need to be repaired by a qualified service technician.

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Try adjusting the viewfinder diopter. There's a little dial just to the right of the viewfinder. Turn it while looking through the viewfinder. You want to be looking at an unfocused view or a blank wall. Turn the dial until the focus brackets are sharp. Make sure you do this with your shooting eye.

while using slr cameras u always see in the viewfinder bcuz slr is a single lence refleime u can see the picture after shoot by clicking on play back option this is a feature of an slr camera

This sounds like some kind of lens flair. Make sure there are no bright light sources at about 45 degrees to the lens and it should correct this problem. If it is not that then there may be a problem with the CCD, the part that receives the exposure. Without knowing if this is a point and shoot or digital SLR this is the best answer I can give.

check on the shutter speed and also the Aperture priority..

Page 20 of your user manual manual explains about each time the INFO button is pressed while in shooting mode. The camera is not a live view LCD screen so after it shows you normal information and then detailed information if you press INFO button again the camera screen will shut itself off. To turn the screen on again you need to press INFO again. This is normal camera behavior.

Shoot 10-15 times hard thats all..

The camera has a mirror lock up feature for cleaning the CCD sensor. You may have engaged it. Check your manual about this function