|Why would you transfer OEM hardware into another case?|
The fact that the new power supply burned out quickly tells me that you bought a cheapie. Generally speaking, a decent quality units costs at least $50 & you have to pay close attention to the amperage specs, especially when installing a gaming card. The GTS 250 is a power hungry card & is rated at 150W under full load.
There is no "nvidia xfs 250" so I assume you have a GTS 250, possibly made by XFX?
The "system fan error" refers to your CPU cooling fan.