make sure your mb bios and chipset drivers are up to date. try downloading and installing newest june update to direct-x.
check that your cpu fan is moving..try msi afterburner and turn the fan on faster). it could be a heat issue with windows 8 driver not spining up the fan to keep the card cool.
For those who cannot get their switchable graphics to work in lenovo or hp, after the win 8 upgrade or clean install, a fix is found and i am giving it here:
1. Goto BIO Setup by pressing F2, or whichever button is configured during the booting.
2. In the Configuration menu disable the Graphics Switchable and make it to Discreet.
3. After that Enable the virtual section below. Save and exit.
4. You are done.
In this method you wont see the Intel HD Graphics in Device manager but the ATI Radeon starts automatically within no time.
You can confirm this by installing AMD system monitor from the AMD site.
Note : If by any chance you cannot configure the switchable graphics in the BIOS then u must download the driver for BIOS from the lenovo or hp website support section. After installing the new BIOS, do the above steps and u r done.