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Did you remember to install the drivers
for both the Intel and ATI? If not get the latest one for it from Acer here, Acer Support: Downloads & Support Documents - Notebook / Aspire / Aspire 4810TG
The one you want is version 8.652.1, and it already has the Intel driver
in it to work with the switchable graphics that you mentioned. I also came across this, Acer Aspire 4810TG « The Acer Guy Forum
where they mention that there is a bios setting to choose whether to use the switchable graphics or only one of them. No idea if yours has that option or not, but if it does and is enabled then you have to use the above driver.
If it is and have no idea if it would work or not, but if you set it to only use the ATI instead of both then it is possible that the latest ATI/AMD driver, http://www.sevenforums.com/graphic-c...ndows-7-a.html
Edit: Should have looked at it before, but just had a better look at the download page for your laptop and checked the FAQ page and found this, Acer Support: Frequently Asked Questions list for Cannot Install ATI VGA Driver v8.612 in Windows XP
so if you have bios version 1.22 or later then you will have that option in the bios. If not and you would like the option Acer has two bios updates available for it, a 1.35 and a 2.35 on the above download page link.