Need more info.
System RAM and Video RAM.
Connection type (dial up, DSL or Cable) and are you on Wi-Fi or a "hard connection"?
I am using Chrome with cable connection.
What version of Windows?
How much RAM does your system have?
Right click "My Computer" and choose "Properties" to see system info.
A slow processor, not enough RAM or not enough video RAM can lead to this. I had a six year old e-machine with a single core AMD processor and only 128mb of video RAM. It wouldn't play movies or other videos on YouTube worth a darn. I could download them and watch offline, but not through a streaming feed online.
My computer was just overhauled. Everything was working fine (sound and
video) until the latest version of adobe flash player was installed.