Question how can i repair this

Jun 5, 2019
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so i bought a prebuild pc lenovo y520
and i took out the gpu ram hard drive ssd and cpu
now im trying to sell the prebuild so i bought new cpu ram and hard drive
the gpu i took from my brothers gtx 970
now the prebuild pc wont post and beeps 3 times and 1 long beep
how do i fix this
the gtx 970 works in my new pc but not in the prebuild
the prebuild dosent have os installed and i cant see anything because no signal on monitor and i tried everything to fix it
 

King_V

Illustrious
Ambassador
The maximum 27 Amps on the combined +12V rails on that 450W PSU is too weak to power a system using a GeForce GTX 970.

27 x 12 = 324
Yeesh, yeah, a "450W" power supply that only provides a total of 324W on the 12V rails? That indicates to me that it's likely to be a very low quality PSU that you probably do NOT want to use for any system that's important to you.