Subject is dark when looking through the viewfinder

Use the largest screen to get a better idea of the focus. Smaller screens lack the resolution to show a slightly unfocused shot - but it will be noticeable later when printed or viewed on a large screen. Of course, these screens eat battery life - so you can use your optical viewfinder whenever possible.

Turn up the ISO...or ...turn up the "exposure compensation"......or turn up the lights...or use the flash.

The finished image looks dark or it looks dark in the viewfinder?
If your question is "the image looks dark" in the viewfinder my answer is it's an F4.5 lens so letting less light into the viewfinder and it will look dark. The big difference will be seen if you are coming from lets say a Nikon 50mm F1.8 which is two stops faster then your F4.5.
If it's the finished picture after you taken it I'd say you underexposed the shot.

Change your focusing setting to spot focus. Then, focus on your main subject, keep the button half-way pressed while you re-compose the shot and then press it the rest of the way. Does that improve the shot?

It sounds like the infamous aperture control problem. I had mine fixed by this place:

http://www.garryscamera.com/

They had it for a couple of weeks, and when I got it back it worked perfectly.

That would explain the darkness if the lens is stopped down. It would seem the aperture control is faulty on the camera body. Normally, the aperture remains open until you take the picture. It is only closed down while the shutter is open.

Like all point and shoot cameras, PhotoPC's viewfinder is not 100 percent accurate and will slightly magnify the subject. The actual picture will always appear to have been taken further away than what the user views through the viewfinder.

Try the FOCUS LOCK feature. This feature allows you to focus on a subject roughly the same distance away from you, then re-compose your picture without losing that focus. Open the lens barrier fully. Look through the viewfinder at the AF Target Mark (the 4 lines in the center of the viewfinder). Position the AF Target Mark on a subject roughly the same distance away from you. Press the shutter button halfway until the green lamp lights. While keeping the shutter button pressed halfway, re-compose your picture, then press the shutter fully.

Try the FOCUS LOCK feature. This feature allows you to focus on a subject roughly the same distance away from you, then re-compose your picture without losing that focus. Open the lens barrier fully. Look through the viewfinder at the AF Target Mark (the 4 lines in the center of the viewfinder). Position the AF Target Mark on a subject roughly the same distance away from you. Press the shutter button halfway until the green lamp lights. While keeping the shutter button pressed halfway, re-compose your picture, then press the shutter fully.

Try the FOCUS LOCK feature. This feature allows you to focus on a subject roughly the same distance away from you, then re-compose your picture without losing that focus. Open the lens barrier fully. Look through the viewfinder at the AF Target Mark (the 4 lines in the center of the viewfinder). Position the AF Target Mark on a subject roughly the same distance away from you. Press the shutter button halfway until the green lamplights. While keeping the shutter button pressed halfway, re-compose your picture, then press the shutter fully.