mac pro 3.1 hang

Hi guys,

recently i have just upgraded the ram of my mac pro to max. 32gb.
and also graphic card - quadro fx 4800 1.8gb flashed.
after upgrading to OS 10.9, i encounter machine hang will surfing the net using safari. i have also updated safari to the latest 6.1.1.

will the cause be the ram or graphics card.?

anyone encounter anything like this before??