something's wrong with my MPC

Yesterday, I uninstalled a bunch of programs and unintentionally uninstalled my Media Classic Player
(and maybe, MAYBE some of the codecs along with it, but I don't know and I don't remember if they are codecs are not)

problem is, after I re-install the newest full versino of MCP (10.5 full), my video's result are.....weird
(note: I haven't installed or update any video programs & codecs since 2011 or maybe 2012.. but I think it's around 2011 where I have to update a codec to run videos in 10-bit back then.)

all of the videos have a "darker & deeper" coloring, and most of the time some or a lot pixels are gone (very obvious in shot-by-shot comparison)
and the problem's worse with old videos (my videos that are before 2010), it's like... I don't know.. not compatible or something? The quality got worse and some pixels are missing....

comparison:

with OLD Codec1    
with NEW Codec1

with OLD Codec2    
with NEW Codec2

with OLD Codec3    
with NEW Codec3

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I've already tried installing KMPlayer, and VLC (the latest versions) and the same problem still persists (as if it doesn't do anything with it)
I also tried uninstalling my 10.5 version of MPC and re-install the program from version 5, 5.5, 6, 6.5... up to version 10.5 again
and the video's still the SAME.......

I have no idea what I uninstalled yesterday (other than a music program Steinsberg and Finale 2010 versions and some other programs I can't recall, including unintentionally uninstalling the unknown version of MPC...)

Does anyone know how I can I fix my computer (or codec, or program...I don't know) so that the videos will be back like when i use the old codecs?
Please tell and guide me on how to do it....

Thank you very much

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addition:
another critical thing i just found out,
when i decrease the video speed (so that i can take screenshots of the video) it has this.... lagging effect
what i mean by this "lagging effect" is that, suppose the video is showing that the camera view is from the soil up towards the sky
(the camera view is going "up"), so in each frame, the picture slowly goes UPWARDS....
but then sometimes, the picture goes DOWN about 2-3 or more frames.... (as if it played the "previous frame" instead of playing the next one)
and then it continues going upwards as usual
(and then that random lagging which causes the frame to show the picture going "down" again instead of going "up")
and this happens to every video file i have

it doesn't work like this previously since i often decrease a video's speed to screencapture a lot of pictures to make GIFs....
but right now I can't do one because of this random lagging effect that screws all of the frames....

I can tell you that "darkened" look is the correct one. Your "OLD" pictures look way too bright, which tells me the range is clearly incorrect in those. The "NEW" pictures look like they're supposed to, with black being black instead of gray. Also, I'm not seeing any missing pixels. Your monitor brightness is probably lower than it should be too, that's why there appears to be details missing to you.

Maybe when you re-installed MPC, it reset your renderer settings. So previously, you were using VRM9 (renderless), which gives a bright and incorrect picture unless you convert it to RGB24 or RGB32 (at least it always did to me).

About the lagging, maybe the administrator will be able to help you with that.

Yes, the NEW screenshots are the one with correct colors. If they look too dark for you, then you should indeed increase the brightness of your screen.

I don't know why you get that weird behavior with reduced playback rate. I would advice to pause the video just before the desired spot and use the right arrow key (= frame step forward) to go to the desired frame.