I'm trying to figure out why usually but not always the Youtubes I watch are so slow resulting in constant buffering. And it could be that different Youtube videos may play FASTER. More than one cause I suppose. I have windows 7 and the computer is quite fast/capable if you look at the properties however it is 3 years old. I have Malware Bytes and AVG installed and I've tried disabling these without making any difference. My home network is password protected. It's 7am and the video I'm watching is very slow so wouldn't the bandwidth be okay? And as I write this the whole computer is slow to load pages etc. Maybe I should address this as just a slow computer? Other times though pages load just fine. Go to speedtest.net and run a speed test several times throughout the day. Record the time you ran the tests and the results (upload, download, and ping). Do this for a few days and SEE whether a pattern emerges, a pattern that shows variation in the speeds between different times of day. And, see whether you can correlate the speed test results with the issues you're having with onlne videos.

Regarding your computer's performance, as opposed to your Internet connection speed, open Task Manager (Ctrl/Alt/Del) and keep in an eye on CPU usage and Physical Memory usage when you experience slow video issues. This might help determine whether there is a general computer performance issue or strictly an Internet connection speed issue.

If you haven't cleared browser history for a long time, do it, close and reopen your browser, and then see whether video performance improves. If you are lax on clearning of browser history, you may need to get in the habit of doing it more often.

What web browser are you using? Have you tried any others? Using IE 8? the latest. Windows Vista service pack 2 I wondered about firefox or google chrome.