Got acer aspire m5100 amd phenom quad core 2.2ghz

[jambopepsi]

Hello,
im am trying to fit gigabyte ati hd 5870 to my sytem but windows 7 boots up then monitor goes back and power light flashes on and off can u help plz

 

[jambopepsi]

Hello,
im am trying to fit gigabyte ati hd 5870 to my sytem but windows 7 boots up then monitor goes back and power light flashes on and off can u help plz

my card details are gigabyte ati radeon series hd5870 im running windows 7 with 8gb of ram new to this so dont no much about what im doing