Help for yosemite install

[ahmed19981]

Hi to everybody,

I want to install Osx Yosemite on  my Computers. I have 2 Computers: 

The first:

- Amd A8-3850 Apu

- 8gb Ram

The second:

- Intel i3

- Integrated Graphics card ( Intel graphics HD)

- Nvidia GeForce

- 4gb Ram

In the second installation is successful startup but remains on a flashing gray screen. however in the first installation to 75% crashes you are indicating that you can not continue the installation.
What do you recommend?

Thanks

 

PS. sorry for my english