All you had to do was put your motherboard into google and first page to come up is Biostars website with motherboard information.
Most AM3 boards can't support AM3+ processors, and this confirms that yours doesn't. http://www.biostar.com.tw/app/en/mb/introduction.php?S_ID=520
With a 1090T there is no reason to even purchase an 8120 any ways, it's not an upgrade except in very few applications because it's not a true 8 core and relies on higher clock speeds to match Phenom II performance.
Benchmarks if you haven't seen any yet.http://www.xbitlabs.com/articles/cpu/display/amd-fx-8120-6100-4100_7.html#sect0
Note I linked to the applications, if you look at the games FX looses horribly to Phenom II, not sure what you use your computer for.