screen flicker

I recently started doing more photo editing on my computer and I noticed something annoying. The monitor has an odd flicker that is not noticable at first but becomes more so after extended use.

I use window 7
display adapter>>>nvidia geforce 6150se nforce430
processor>>amd sempron
Is this a sign of the monitor beginning to fail? Is it a power supply issue? Is there a way to correct it without replacing the monitor?

Also - what is a fast graphic viewer? I use PhotoShop and PaintShop Pro but they take a while to open. I'm looking for a program that opens graphics fast for simple editing and viewing.