Unless something is broken in your Windows 7 installation, there are (at least) 3 ways to select multiple files in a Windows Explorer window. The methods work best when the view is set to "Details" but can work with any view:
- Left-click once to select the first one. Press the SHIFT key. While keeping the SHIFT key pressed, left-click once on the last one. This selects multiple contiguous files.
- Left-click once to select the first one. Press the CTRL key. While keeping the CTRL pressed, left-click once on each additional file to be selected. This permits the selection of non-contiguous files.
- Left-click on an empty area in the Windows Explorer window, preferably below and to the right of the last file in the list. Keeping the left mouse button pressed, drag until the selection area includes all desired files, then release the mouse button.
You can combine these methods. For example, you can select a large number of contiguous files use the SHIFT key and then press the CTRL key and click any files that you want to de-select.
If those methods don't work:
What version and service pack of Windows 7 is installed?
What is the name and version of your antivirus program? Has it always been kept up to date?
What are the names and versions of all other "security" programs installed?
Have you ever used a "registry cleaner," tuner, tweaker, or the like?