The normal "select" in Word is to click and hold down the mouse left key while you drag over the text.

To select contiguous longer sections, you can place the cursor at the beginning, and hold down the Shift key while you click at the end.

With drag and drop, holding the Ctl key down while dragging should Copy the selection to where you drop it. (The equivalent of Ctl-C to copy and Ctl-V to paste.) Holding the Alt key while dragging will MOVE the selection to the drop point. (Equivalent to Clt-X to cut and Ctl-V to paste.)

Holding down the Control key while you click - with the most common settings - usually will select an entire paragraph, but if you try to drag the mouse without releasing the mouse key, with Ctl still held down, it thinks you're changing your selection and may drop the entire selection.

If you need to select multiple non-contiguous bunches of text, the only simple method in older versions is to use what Microsoft calls the "spike." You can copy a selection to the "spike" using Ctl-F3, and all of the selections you copy are "added on" in memory. Ctl-Shift-F3 then dumps selections from the spike (into a document) but they do come out in reverse order (LIFO) so you have to plan ahead or expect to cut/paste to sort the "dump." The "expanded" clip board in latest Windows/Office versions allows you to have multiple "copies" in the clipboard, and to select from the ones available, so I'd expect use of the Spike is less known for newer users.

A commonly encountered interference with normal cut and paste or drag and drop is the accidental invoking of "Sticky Keys." In this mode, once you press the Ctl or Alt key, the program responds as if the key remains held down, until you "complete an executable command." This is an "accessibility aid" for people who have trouble working multiple-simultaneous-key combinations. The default "quick key" to toggle this function on/off is fairly easy to produce by accident - pressing the shift key five times in a row.

(I spent about a half hour confirming the short cut in Vista/Office 2007 UnHelp since I haven't had that accident recently. All "Help" searches lead to half-hour video training programs that waste your time without telling you anything related to your query, on the standard Microsoft assumption that "only idiots use Microsoft's latest products.")

There are a couple of other "accessibility" options that can produce somewhat similar unexpected behavio(u)r, and any of several could have been "invoked" accidentally. Or you may have had a key that was mechanically "stuck?"

John