The easiest thing to do would be to reinstall Win7. After the initial install and reboot...go to Windows Update and install all available updates and service packs (there will be a 100+).
** Windows 7 and Windows 8.1 must be fully updated before attempting to install any AMD driver. All 'critical', 'recommended', and 'optional' (no language packs,etc) updates as well as any Service Packs (SP) must be installed before any attempt to install graphics drivers. If you do not get this message .... keep installing until you do:
When you get a message that there are no more updates available then install the latest/last AMD driver (I would use the 16.2.1 version):
A6-3420M with Radeon™ HD 6520G Drivers & Support | AMD