Try to clean the contacts on the card, Im no sure if you can just use some alcohol rubbing. If that does not work, you're card might be faulty. Best of luck
eMachines ET1161-07 is listed as having a 250 watt power supply.
HD 6450
System Requirements:
■400 Watt or greater power supply recommended
http://www.amd.com/us/products/desktop/graphics/amd-radeon-hd-6000/hd-6450/Pages/amd-radeon-hd-6450-overview.aspx#3
Mine actually has a 400 watt dynux psu (DX-400WPS) which has been working perfectly fine with my computer.