When working in PE7, the mouse is acting as though it's mode has somehow been changed. When I hover over the arrows of scroll bars, it starts scrolling without me clicking on the mouse. I also am locked out from moving any clips on the timeline...I just get a no sign (circle with line through it). This only happens in one particular PE7 project on this computer. I feel like I've seen it before but can't remember the solution. It's as though a couple of keys were bumped which happen to be a shortcut combination to alter the way the mouse works.
Though it doesn't require that large a dose of resources, when they are running low, the mouse can certainly act wonky. The tips in this ARTICLE might be useful for getting your computer ready for an editing session.
Next, there have been issues with the MS InteliPoint mouse driver and displays in Adobe programs. Going back some years, these would cause the GUI to flicker violently. That was cleared up with later versions. Then, a newer driver caused parts of the GUI to not display properly. Do you have the InteliPoint mouse driver? If so, try removing it and replacing it with the generic Windows mouse driver would be a good test.
There have been some reports of the Logitec SetPoint driver causing issues in Adobe programs. Again, the test is the same, replace that with the Windows generic mouse driver.
Since your behavior seems Project specific, I'd look closely at the first suggestion. A large, or resource intensive Project can be a resource hog. Can you tell us the details of your problem Project and also the specs. of your computer? That might point someone in the right direction toward finding a "cure."