Windows 7 can't see my backup files

I'm not sure of were is the right place for this topic but i`ll try here.
Hi
I have just backed up a full image (using back up and restore) of Windows 7 Ultimate Evaluation copy.Build 7100 "Which I have had no problems with what so ever" to my 500gb Maxtor External HD .I then did a fresh install of Windows 7 Pro ,the install went fine untill I tried to restore my backup from my External HD.
Using backup and restore it tells me "Windows could not find a Backup for this computer" when I click on "Select another backup to restore files from" it see`s nothing but when I browse network locations it see`s my External hard drive and the files but when I click on the files to restore it says "Windows was unable to find any back up sets".
At this point I should admit that during the installation I changed the name of the pc (not smart) and after a few attempts to retrive the backup I changed the name back again,but still got the same response,I couldn`t find much on the web but I thought (using my vast computing knowlege"NOT")that if I reinstalled the Evaluation copy then maybe I could gain access to the backup(on my External HD) and restore it and save manually what I needed,
I have done this and still have no backup files only now it doesn`t see the External HD at all.
Just to give a time line
Orginal operating system Windows XP Media Center Edition
Upgraded to Windows 7 Ultimate (Evaluation copy build 7100)
Backed up operating system Windows 7 Ultimate (Evaluation copy build 7100)
New operating System Windows 7 Professional
Paniced and reinstaled Windows 7 Ultimate (Evaluation copy build 7100)
I know its a bit of a mess.So now I understand the little knowlege is dangerous thing tale.I would like to reinstall Windows 7 and gain access to my backup .Any hoo I hope I`m in the right place to ask this question and hope that some of you kind people will help...Thanks in advance

I think it's because you probably did a fresh install over the partition that the backup was on. Clean installs format the drive, keeps windows.old and wipes out everything else. Your backup right now is probably gone. Unless you stored the backup on a separate partition.

Sorry I forgot to say alot of stuff like backup is on external HD in my post please check out the updated version

Looks like you are another victim of the complicated and partially defunct windows backup and imaging facilities. If you want to make your life easy and always understand what you are doing at each step of the way, I suggest you use free Macrium for your imaging needs. I can guarantee that it works - always.