My computer is slow and annoying.?

Its taking about 5 minutes for it bring up the Yahoo front page when first switched on. I have took out all the history and any temporary files. I have also de-fragmented it and run it though AVG and nothing untoward was found. A quick check on my broadband speed showed a10800 kbps download speed and 811 kbps for the upload speed. Every move I make with the mouse takes between 1 to 3 minutes to carry out. Has anyone any idea what can be done please. Regards, Malcolm