Boot windows 8 into safe mode with networking and see if it's slow.
If it's not then you might have a lot of programs running that are unnecessary or you might have a virus.

Using the Run command type   MSCONFIG  and press enter.  Then click on the startup tab and see how many programs are listed with a check mark next to them.  Remove the check marks in anything that isn't your anti-virus.  It will in most cases then not load that program at startup BUT it doesn't remove the program and the program is still usable when required.  If you find that you want a certain program to run at startup then put the check back.

Note, reboot after changing MSCONFIG.