DVD drive letter D changed to J How can I get it back

I have a Dell XPS 8700 running Windows 7 professional. I just noticed today that my first DVD drive letter went from D to J. One of my external hard drives used to use the letter J. Now it is D. The DVD drive appears to work OK, but it may be a problem when I do backups using my external hard drives with Acronis. I am not sure when this drive letter change took place. I tried doing a checkpoint restart from a restore point taken 3 days ago. Same problem. Is there some way to get the drive letters back to they way they were? I am used to my two optical disk drives being D & E. Now they are J & E.
Charles Ranheim

Thanks for your suggestion. I am not a PC guru, so please be patient with me.
As I said, my first optical disk that was D, became J. When I power on my two external hard drives, one of them now comes up as drive D. Would it be safe to leave the external HDs turned off, then change my first optical drive from J to D? I would hope if this can be done, when I turn on the external HDs, the one that was now D would be reassigned back to J. Does that sound OK? I sure don't want to do something that buries my machine where I cannot recover it. I do not know when the drive assignments changed. I can say, however, they were OK at the end of last month when I did an Acronis backup to the external HDs.

Thanks again for your time and interest. I really appreciate it.

Charles Ranheim

I never liked changing anything in the registry. It appears like the procedure in option 1 step 5 would allow me to change my first optical disk letter from J back to D with the remote HD's powered off. Then, I was hoping that when I turn the external HDs back on, the one that had the D designation would seek another letter on its own (Hopefully J) If it picks a different address, I thought I might be able to change it back to J with the same option one step 5. Am I missing something?

Charles Ranheim

I decided I wanted to try Option 1 step 5, but was afraid to do so without contacting Dell Support because my PC was still in warranty. All I wanted to do was to change my optical drive 0 back to letter D. The lady I finally got to speak with in India did not think that was a good idea, and that I should just accept the new drive assignments. (My drive D had changed to J, One of my external HDs changed from J to D) The external HD change would affect me running Acronis backup. She recommended I just accept the way things were. While she was connected, I changed optical drive 0 back to D from J using the Disk management screen. After doing this, all the other device letters went back to normal. Problem fixed.

In trying to figure out how this all happened in the first place, I thought of the possibility of an intermittent failure in optical drive 0, where it was not immediately detected on power on, and failed to be auto assigned letter D, but later was assigned letter J. This may have caused the chain reaction of changing the other drive letters as well.

I certainly want to thank you all for your interest and responses to my problem. I learned a lot from this experience with a PC. I worked with IBM for 40 years as a large system support specialist, but had no real experiences with PCs