Most movies (60%) I view on the PC are dark (store bought and downloaded). It seems to be the in thing in hollywood to shoot the movies too dark. My wife rants about this too.
When you reformatted all of your video card and monitor adjustments made previously were erase. So you need to re-tweak for the viewing level you like
1) You need calibrate your monitor. Google "monitor calibration". Ignore the ads for software. All you need is the pictures on the free website. Monitors dim and drift as they get older. Adjustment should be checked every 6 months. Adjust the contrast and brightness at the monitor controls. That way if you reformat nothing is lost.
2) You need to set the Gamma for your video card. Displays (CRT and LCD) do not represent light intensity the same way nature does. They are non-linear and drift with age. A different video card may also set the curve differently. My monitor is getting old and my current video card seems to have had a too high Gamma. I just adjusted it last night and when playing BF 2142 afterwards went WOW. All the details (like where the guy shooting me was hiding) is now visible.
The video controls on the players allow you to adjust brightness and contrast but the results are disappointing compared to adjusting the monitor and video card correctly.