Prompted to choose where to open new application. NO LUCK. I broke it.

Question

I have had this problem for a while. Sometimes I cannot open a newly downloaded program. Sometimes there will be a system pop-up stating, "Bluetooth hardware not found". I have no idea why most of these files would have anything to do with Bluetooth. I fear I mixed something up in 'launch services' as I have been told. Below are links to past threads where I was trying to sort out the problem. Unfortunately they have been archived and I cannot respond to these original posts.
*This latest problem was with a dmg file.* I downloaded the dmg file but when I went to open it a system pop-up prompted me to 'select an application(I think it was) to open the file with'. This does not always happen. More often when I click on the newly downloaded program it just opens it up. Since this was a reverb plugin for use with Logic Express I tried to open it with Logic. This didn't work. Finally I selected 'disk utilities' hoping this would work and it does SOMETHING but it doesn't open it. Disk utilities opens up and I can see it written under my hard drives but I'm sure this is not what I wanted to do. I am obviously in over my head but I need to get this resolved. I've been ignoring the problem for too long and I am missing out on a lot of great programs because I have somehow messed my computer up. Any help would be greatly appreciated.
Below are links to the archived threads mentioned earlier:
Cannot run/open new programs. Pop-up says "Bluetooth hardware not found" ?
http://discussions.apple.com/thread.jspa?threadID=1302568&tstart=0
Cannot open newly aquired programs- strange warning pops up
http://discussions.apple.com/thread.jspa?threadID=1062685&tstart=0

Answer 1

Hi, thanks so much, Limnos.
Yes I did as instructed in the other thread. Here is a step-by-step of what I did and where it takes me: I hit control> click on desktop icon >get info> verify "open with" is set to diskImageMounter. It already was. I did not have to change it. There is the option to open with diskImageMounter(default) or disk utilities(disk utilities was not an option at first. This i'll explain later*). I then select open and the program appears in the finder. I click on it and 'disk utility' opens up with a smaller screen labeled, "New Image from folder" prompting me to 'save as', 'where' to, what 'image format' and 'encryption'.
Each new program opens up in disk utility now.
Before it opened up automatically in Disk Utility when I clicked on the program in the finder, I was prompted to select an Application to open it with. I tried various things, for example, Logic Express, as the program was a VST plugin for use with recording software. I could not select 'open' with Logic. I tried 'disk utilities' in my ignorance and that is where it took me and each subsequent time I try to open the program from the finder. *When I first opened it up in disk utilities I 'fiddled around' and subsequently each time I go to open this program there is the option to open in diskImagemounter(default) or disk utilities, however when opened it is always opened in disk utilities even though the extension in the getinfo is still dmg.
Another new program, this one a Stuffit, opens up in disk utilities.
I'll start looking into Onyx. If you think I should back up my computer beforehand that's a whole other can of worms I'll have to look into. A few months ago I bought an external drive and backed everything up but now I'll need to figure out how to do so by somehow only backing up only new files and not everything again in addition to what is already backed up. I hope that makes sense.