The possible reasons for buffering are as follows:
1. Insufficient memory on your computer. (Unlikely with a modern PC).
2. A program on your computer is hogging most of its memory or processing power, leaving insufficient capacity to handle the processing of the video stream. (That's rather more of a possibility but still fairly unlikely).
3. Insufficient bandwidth, either due to a poor telephone line to your router or a poor wi-fi signal to your laptop. (That's by far the most likely).
See my post here for a way to test your available download speed (and further relevant information):
http://www.theanswerbank.co.uk/Media-and-TV/Question1331060.html
To see if a rogue program is hogging the CPU, right-click on the task bar at the bottom of your screen and then on Task Manager. Click on the Processes tab and look down the CPU column. Most of the figures should either be '00' or in single digits (e.g. '02'). Anything in double digits should be regarded as unusual. (If you find anything like that, tell us what it is and we'll tell you how to deal with it).
It could also be worth trying a malware scan to see if anything is causing problems. See my post here for the necessary instructions:
http://www.theanswerbank.co.uk/AB-Editors-Blog/Question1331113.html
However it's still most likely that the fault relates to a poor service from your ISP or a poor wi-fi signal. Try connecting your laptop to your router with an ethernet cable, instead of wirelesly. (Your router should have been supplied with an ethernet cable. If you've not got one, Poundland will sell you one for a quid). If that improves things (but you don't want to permanently use a cabled connection) you might need to change your router's channel. However I'll leave those instructions until you've found that they're necessary.