Upgrading the Compaq Presario is going to be less expensive if you don't need a copy of Windows 7. And you'll get a video card that's quite a bit better than the HD 5450.
Probably best if you go ask that question over in the section of the forum that does PC upgrades and new PC builds. Systems Forum
Look around there for a bit and see what other people are talking about.
You'll get some ideas on how to ask your own questions. Something like: $300 upgrade or $400 new build?
Give them the link to your current PC & monitor, plus the $400 CyberPower PC and let them suggest different options for you to think about.