horrible quality of low-res vids on fullscreen

[Hawkera]

Hello all, recently I re-installed my windows and after that all low-res videos 640x480 for example, look extremely horrible when played on fullscreen, it looks very pixelated(like minecraft), before it wasnt like that, it was way smoother, I did some research and found out it had something to do with codecs, I played around with the rendering mode, with some of the renderers there it worked, it fixed the quality, but Subtitles werent working or there were huge black bars everywhere.

I honestly don't know what to do, downloaded some divx 10. something codec but that broke everything, downloaded a xvid codec, didnt help at all...

Please tell what to do to fix this... Before the reinstall all options, codecs, renderers were all the same, and I have no idea what is causing this problem after the re-install.