Hello, thanks for the answer.
After reading on Adobe's forums for my flash video's stuttering problem, i reverted my flash version to an older one that seems to be working, it's a temporary workaround, and i really have no idea where the problem comes from, can't be sure it's either flash or the drivers.
3375 drivers really don't work on numerous HP systems, i have seen the problem being reported a lot of time on HP's forums.
3345 seems to work fine, as i said, i have no way to test external display, so i can't comment/report about it working or not.
My dxdiag is in attached to this reply, if you need any further log, will be pleased to help.
Thank you for your help in this issue.
P.S: Here is a link to the thread i found on Adobe's forums, not sure whether it can help or not, but seems it contains a workaround, might help other users.