Youtube file possibly infected PC with Virus, Printer won't print in Black

My HP Photosmart 4200 won't print in black & the cartridge is 1/2 full. Monday evening I stupidly downloaded & installed a 'typing programme' my younger brother e-mailed me. I later found out he got it on YouTube & some place called mediafire? I shortly uninstalled it but too late.

PC: Windows Edition: Vista Home premium 32x; Anti-Virus: Norton 360

Things I have done to date:
1) Deleted the e-mail, uninstalled & removed any files on hard drive I could find of this programme & Emptied Recycle Bin.
2) I ran a 'Comprehensive Scan' in Norton 360 but it didn't identify any major problems. Only a few Cookies. What are Cookies?
3) I ensured cartridges are in correctly.
4) I ran a 'test page' on the HP printer to check if printer is functioning correctly. It showed perfect & definite 'coloured images' but absolutely no 'black images' or even faded images.

Printer was functioning perfectly last week before this file was saved onto PC.
Any advice to fix the problem would be greatly appreciated.