Laptop virus cannot log in windows

[howdiedoodie]

I am also having problems..i can't log on,it starts up,but the users doesn't show up..

 

[howdiedoodie]

i think there's something wrong,i've done everything i could,run diagnostics, power cycle,run in safe mode..i really can't get in..would you please tell me how to format my laptop??it's a Compaq Presario CQ40