Recently, I upgraded from an Nvidia 6800 to an HIS 4670 (1gb 128bit). After reformatting my hard drive and installing the drivers, I noticed that there were lag spikes every now and then. For example, my mouse cursor would be traveling smoothly and then suddenly hit some lag and go slowly. When I right click, my whole computer would lag: if I had music playing, my music would lag as well. Also, my screen blacked out frequently. At first, the screen would dim down. Then the screen would go black (monitor and computer would still be functioning), and I would be forced to either put it on hibernate and turn it back on, or manually restart my computer. If I were to put my computer on hibernate and turn the computer back on, my screen would still sometimes black out (in the same manner as it did before). Also, Windows would take an oddly long time to load up with the 4670. My computer would be stuck on the "Windows is loading settings" screen for ten minutes (or even longer), before going to the "Welcome" screen (plus another five minutes of waiting). After getting tired of the said problems, I switched back to my old 6800. Everything works fine - no lag spikes, Windows boots up smoothly, no black screen, etc. Unfortunately, playing games lags on the Nvidia 6800 but not the Radeon 4670. Could this have been caused by a CPU bottle-neck (I have a Pentium 4 3.4 Ghz processor), an insufficient PSU, or something else?