Quicken 2005 Home & Business lost data

I've used three versions of Quicken Home and Business over the years and never had any problems. I opened the program one day to find that my bank check book register showed that I was $15,000 in the red where I should have been about $2000 in the black. Since this account reaches back over several years I can't easily find where the problem lies. I've also discovered while doing Reports for taxes that numerous transaction entered in the check book register have vanished -- like my monthly payment for health insurance -- a whole year and halfs worth. Has anyone else had this sort of problem. Do you have any suggestions for dealing with apparently lost data?