N72 hangs after starting..

i had n 72 in last nov. yesterday i downloded some antivirus software called pandaantivirus.on memory card but i got hanged up while installing hence i rebooted my phone,now onwards my n72 gets hangs.desktop appears on the screen and it goes white blurr.. today i formatted mem.card by putting it on pc. still problem persists.. i have to switch it off by removing battery since no buttons are working...
kindly help me out.