need help with trojans on site

I need help with my site, first of all, my site is coming up with a blank white page, which is minor becasue i think its just some codes that need to be modified, but my real problem i shtat my site has trojans, I do not know how to get removed, i have downloaded a number of virus programs that detect them but dont repair them, and some of the programs didnt even detect them, i dont know what im doing, if there is someone, that could handle this for me to get rid of the trojans and then correct my site, it would be great, thanks