Usually there are problems when the available RAM is really low, but I doubt the problem can lay there, also my PC (a really old mummy) is able to switch between applications without problems (at least between BSplayer and Windows Explorer)...
You can try to see if (by running task manager: CTRL+ALT+DEL) there are suspicious processes running in the background that may slow down your system..
Does it happens with every video file? Codec used by BSplayer to decode it? Nero?
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