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Is your Vista 64 bit or 32 bit. Either way, your Premiere Elements 12 is a 32 bit application with all the resource implications that go with running in a 32 bit system or in the 32 bit compatibility mode of a 64 bit system. So, first question, what is a description of your computer resources, starting with installed and available RAM and free hard drive space.
Does the problem exist with and without the antivirus and firewall(s) disabled? Do you have McAfee antivirus program?
Have you updated Premiere Elements 12 from 12 to 12.1 Update? If not, please do so as soon as you can get into an opened project (Help Menu/Update).
Pending further computer information, let us try deleting the Adobe Premiere Elements Prefs file and, if that does not work, then the whole 12.0 Folder in which it exists. I am not sure of the path in Windows Vista, but in Windows 7, 8, or 8.1 64 bit, the path is
Local Disk C
Users
Owner
AppData
Roaming
Adobe
Premiere Elements
12.0
and in the 12.0 Folder is the Adobe Premiere Elements Prefs file that you delete. If that does not work, then you delete the whole 12.0 Folder in which it exists.
Be sure to be working with Folder Option Show Hidden Files, Folders, and Drives active so that you can see the complete path cited.
Also please review the following
ATR Premiere Elements Troubleshooting: PE12: Premiere Elements 12 Editor Will Not Open
Look at renaming the SLCache Folder first.
We will be watching for your follow up.
Thank you.
ATR