thanks ill look into the 5450, i bought a 5570 but it didnt work with my power supply
It probably didn't work because it's a PCI-Express 2.1 card and you tried installing it into a system that has a PCI-Express 1.x slot. Power requirements had nothing to do with why it didn't work.
The DC7700 is an old system, built in 2006, and has a PCI-Express 1.x slot. Because it's a pre-built, it likely never received the required BIOS support update to allow the PCI-Express 1.x slot-equipped system to recognize and initialize PCI-Express 2.1 cards. (Manufacturers only issued such updates for certain supported
systems in 2009, which is when AMD adopted the 2.1 standard and released its HD5000-series cards.) Unfortunately, all AMD HD5000-series cards (including the HD5450 you're considering) are built using the PCI-Express 2.1 standard, meaning none of them will work in a PCI-Express 1.x slot-based system that didn't receive such an update.
As for upgrades that may actually function in that system, you'll have to look for something from the previous generation - the HD4000-series. I've seen several people successfully install low-profile HD4650's in such systems, and even a few install low-profile 9600GT's in them. However, those cards are extremely hard to find (read as: pretty much non-existent) presently.