need help from programmer or smart computer guy, cyrix and others who know stuff

[Zezima]

So basicly i received a message from my internet provider that my computer is infected with "netbios_reflected_ddos kljsfjlksdjfljslj" something, i have NOD32 antivirus (legal version that was paid for and it keeps updating) its allways on, i did not download or instal anythin in the past month. (received the letter today, it sayid that last active sht was 2014-05-10). Any ideas how can i get rid of this ddos bullcrap from my computer? Sometimes it gets laggy as fk (i read somewhere thats when my zombie computer is ddosing somethin).

I scanned it few times, found no infected files, what should i do next?