The first minidump probably wasn't recorded properly/partially corrupt and had 0xA error, which can be caused by a bad / misbehaving driver.
However, the other two dumps pointed at ATI drivers (ati2dvaa.dll) with 0x50 error; you are using driver released in April (probably).
Please download Driver Sweeper or Driver Cleaner Pro (both are free and easily available). Then uninstall currently installed ATI catalyst drivers, reboot your system. Run Driver Sweeper or Driver Cleaner Pro and remove any left over ATI driver files. Then go to AMD/ATI's site and download latest ATI drivers (i.e. catalyst 10.6) and install these.
I hope that will solve your issue, please do keep us updated, and if you need further assistance. Regards