The Stamina/Speed switch on my VGN-SZ5XWN/C model vaio laptop does not seem to work. It stays stuck on stamina, which means it runs on intel graphics rather than the nvidia ones that are used for best performance. When I flick the switch to 'speed' it just keeps the 'stamina' side lit up (LED). Even after restarting the laptop nothing changes. Can somebody help me with this problem? Thanks in advance.