Your system has a 305w power supply (PSU) and the recommended minumum PSU for the 5450 is 400w. It might actually work, but I would not recommend it. You should upgrade the PSU first.
For more information about power supplies for video cards, see the middle of this page:http://www.upgradevideocards.com/criteria.html
A good PSU upgrade option for the HD 5450 would be this one:
Antec High Current Gamer Series HCG-400 400W ATX12V v2.3 / EPS12V v2.91 80 PLUS BRONZE Certified Active PFC Power Supply - $40AR with free shipping:http://www.newegg.com/Product/Product.aspx?Item=N82E16817371046
But I recommend spending $10 more to get its 620w big brother that would enable running mainstream gaming video cards:http://www.newegg.com/Product/Product.aspx?Item=N82E16817371048
Note that the HD 5450 is for general computer use such as office applications and movie and video viewing but not for 3D gaming. The site linked above for power supply information also has other pages about gaming and non-gaming video cards you might want to peruse.