GTX 550 TI Performing Badly

[archon61]

I recently upgraded my system with a MSI GeForce GTX 550 TI Cyclone II from a Radeon HD 4650, along with a 500W CoolerMaster PSU. But all my framerates have dropped after installing the GTX 550 TI and I cannot even run the original Guild Wars on maxed settings in 1920x1080. Whereas with the Radeon I could do so with no problems. I found the same thing with League of Legends, Skyrim, and GTA 4. Is something from my system bottlenecking the GPU?
Thanks.

System: HP Pavillion Elite e9200
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c01916917&lang=en&cc=us&contentType=SupportFAQ&prodSeriesId=3999455&prodTypeId=12454

 

[bwf1975]

Did you uninstall all old amd drivers before fitting new card, old drivers can cause this problem.
Use driver sweeper to remove all amd drivers then install clean nvidia drivers.

 

[archon61]

That worked, thanks!

 

[archon61]

Best answer selected by archon61.