Hi,
I have been in the usa since 1996. From 1996 to 1997 I had a J1 visa and after that I had an F-1 visa (student visa). From September 05-July 06 I was working with my OPT under my F-1 visa and, finally, in August 06 I got an H1B visa (three years) for work. I have spent most days of these years in the USA. I am single. For the last 4 years I have been filling up 1040 and form 8843 (statement for exempt individuals... ). However, I have been recently told that, actually, I should have been filling up 1040 NR. Taking into account the information I just gave you, which documents I should fill up this year? Do I need to fill up 1040 or 1040 NR? In both cases, do I need to fill up form 8843? Did I do it wrong the previous years?
Thank you so much in advance.

If you have been in the U.S. continuously since 1996, either on a J-1 or F-1 visa, then, starting in 2001, you were a resident alien.

The filing of Form 1040 starting in 2001 was correct and proper for you. Continue to file Form 1040.

Form 8843 is no longer required.