I used Bitdefender Internet Security for 4 months and when I scan it will get some viruses but didnt delete it. It says 'no action'. I already updated it but still it doesnt clean/delete the viruses and trojans.

before scanning, you should config the actions when BD found an infected file, a suspect file...
it is usually have 4 options: take no action, disinfect files, delete files, move files to Quarantine
after scanning, BD will try to do the action you have configed before, if it fell, it will ask you again (may be you have chosen Take no action)

note that BD can't disinfect all virus, you will have to send them to BD
and I suggest you moving the virus to the Quarantine before deleting, somethimes you can lost your important files
the most popular way that virus is make a copy of itself and run with your windows. Open the "System info" tab in Privacy Control, take a look to find out the strange item (name and publisher), delete it to make sure it won't start when windows start and then delete it in your hard disk.
scan again if you want

This is because not al viruses can be detected or deleted by your anti virus porotection. This has happened to me it has sed cannot delete. Sometimes it will tell you what file it is located it in look in that file and try deleting it manually. p.s this dosnt always work depends on what virus you have.

try avg, or try an online scanner...
avg is free but avg is also one of the best scanners out there...