The reason the system gets messed up is because of the Lenovo special PSU used. If you think yours is faulty you will need to xontct support and find out what the
After further research on upgrading to a 660/760, I say no,
should only be attempted if you are fairly competent at electrical reassignment of the PSU plugs wiring.
The simplist is to use this converter to get main power to the MB, > http://www.amazon.co...r/dp/B000KKKGG8
but, without swapping wires around on other PSU plugs, you would loose all LEDS on the case front switches and probable the actuarial function, also no function of the Power Phase Switch.
A 550 watt PSU with the nec PCI-E connections would be more than enough to support a 660/760 video card. You would still need to physically measure the dimensions of the existing, to make sure a replacement would fit.
You could sell it and build your own.
Use as many parts as possible with a new MB, PSU, new OS, then sell the leftover parts individually.