I think you can have a better idea of what is your problem by opening Windows Task Manager:
Right-click the taskbar, and then click Start Task Manager.
Go to the process tab and order by memory usage to see which takes the most CPU & Memory usage.
You can kill some **unessessary process**** and see if it solves the problem. If it does, then you will know which one was in cause and investigate further to finally maybe uninstall it or deactivate it from windows startup.
If it don't work, try comparing which processes are running/not running between Safe Mode and normal mode (take a screen capture of it, it is easier to compare that way :) )
**unessessary processes includes all processes specific to the user (has your user or others usernames next to the process) running, excluding Windows official processes and SYSTEM Processes necessary for your system to work correctly
Hope it helps.
Try turning off firewall and anti-virus, which would normally be disabled in safe mode. If you get your speed back, turn them back on, then look for an alternative FW/AV solution with lower impact. – AFH – 2014-06-21T22:11:15.980