I had the similar problem like "green screen problem" that other users are talking about ( in my case not a green screen but black with fluorescent-like color,something like that ) and I try everithing posible way to solve it but with no succes
From Media Room window all video plays perfect but from timeline is horror!!!
Snapshot is also perfect,only playing video from timeline has coruption!
I try changing every settings and configuration also updated it to newest version,but nothing helps!
Try on HD and SD video files with no succes!

I have Win.7 32bit---------NOT 64!!!
AMD Athlon64 X2 5400+, 3,0gHZ
3 GB of DDR2 RAM ------ONLY!!!
AMD Radeon HD6790,1GB GDDR5 RAM

What I do?
1.Uninstall MAGIX produtcts
2.Reset VLC media player preferences and cache files
3.Restore "Factory defaults" settings in "AMD VISION Control Center"

Don't know what of above tree things causing problems ( in my case probably MAGIX conflict with Power Director,but in your's case,who knows,try to uninstall other Video programs)

PS.PD-9 is more than capable to run HD Video on that low-level sistem!!!
See it for yourself in Task Manager how much RAM is consumed when PD-9 is running and you see that 3-4 GB of RAM is enough!!!
Of course, the extra RAM is only good thing for 64bit sistems but I have 32bit and PD-9 working just fine for me
More important is your procesor and grafic card.

Hope that you will solve your problems like I did

Sorry for "gramm" mistakes
Regards,

Andi