These are the causes
...Orginal codec of video files are not mainstream or use high bitrates. Convert to more common avi, with mpeg4 compression not .264 and mp3 audio before watching vids.
...Or could be computer doesn't have enough harddive or harddrive is too slow for videos...and if you only have a x32 cpu and 1 or 2 mb of memory then its hardware related try an 8gb usb flash drive as a ram drive...This process is called Readyboost...the computer has to dig less into harddrive(they (Microsoft) know harddrives are slowest part of computer) and when program memory is full it also uses Readyboost. Can google howto. Try out defrag harddrive also.
...If your using x32 Windows and you've never reinstalled it...there is so much old software that it takes a while to look it up when you want to do something even after uninstalling software. Try out defrag harddrive before settings out to reinstall windows.
...If your hardware is good then unload Windows of stuff that runs all the time...virus detection, internet firewall and close all programs but Videopad, including media player and internet(internet pages use internet even when idle). Some advanced Windows stuff that can be closed click control panel then click administrator tools...google these...component services,services, and task scheduler.
Good luck.