I have a strange problem on my dell n5020 with 4 gb rams and core i5 processor and ATI HD5470 graphics card ... I tried several games on it .. PES 2010 worked perfectly on all settings without even a slight lag and on COD 4 it worked very smoothly on default settings . Today I turned on my lap to play PES but it seemed laggy on medium and high so I ran COD 4 on the same default settings I was running before to find out it's very laggy . What could be the issue ??? Please help !
Did you update drivers? Sometimes people let windows vista/7 update their video drivers automatically. You might have unknowingly updated to 10.9 and it could have slowed your gpu down in that particular game somehow. ATI isn't very consistent with "good" driver releases most of the time so I wouldn't be surprised.
Using Everest ,I found out that the GPU clock and Real clock are lower than original and I found info about ATI power play so I plugged the lap into electricity and the performance went up again , So I checked the Catalyst control center and I found that there are power play options set to maximize performance when plugged and maximize battery life when unplugged .