It is quite old issue, however once again happened to be a problem after fresh reinstallation of Win 7 (disk format) and Aero not working at all. Transparency also disappeared.
Three days looking for new driver
Maybe someone has the same problem - so it is solution:
1. starting from standard VGA installed by win 7 during system installation process
2. install old driver for for XP (delivered by notebook producer); it results with better resolution but not aero and not transparency.
3. download driver for Radeon Pro 9700 - catalyst_8-31-100_vista32_rtm
4. unpack it - it creates folder ATI/SUPPORT/catalyst ...
5. go to control panel, dvice manager, and update manually driver for graphics card browsing to this folder described above.
6. it updates driver asking in the end for restart,
7. restart - Aero is again !!!
maybe it is possible to bypass step 2 but I am not sure.