im on my desktop computer and it happens pretty often that , when im watching a video it stops in the last 10-15 min. where i dont have such problem with my laptop computer./
Unfortunately it's pretty much impossible to diagnose this sort of thing remotely. The most likely issue is that your desktop, for some reason, isn't downloading the full videos, but it's really hard to say why this might be; if you're downloading the videos, I highly recommend using a download manager with it like http://www.freedownloadmanager.org, but if you're watching the Flash videos it's a lot harder to say why this might be -- make sure your browser is updated and you are using the latest versions of Flash.
Hope this helps,