Two posts earlier, the OP answered my question and stated that he tried both a wireless and wired mouse. Therefore, the problem is not the mouse. Here's another idea. Burn a copy of a live-bootable Linux to DVD or USB flash drive. I like and prefer Linux Mint, but there are smaller distributions available (http://www.damnsmalllinux.org/ -- haven't use that one). Boot the PC off the live CD/USB. Does your computer still have the mouse issue? If so, then it's a hardware problem.
Enter Safe-Mode and notice whether the problem persists. This will narrow your focus. Also, all virus/malware scanners are not created equal.
Didn't see your post. Then I think it's the mouse pad problem. The OP just needs to use a non-transparent mouse pad.
Thanks for all your responses. My mice/mouses are trackballs so mouse pad not a factor. Anti-virus - I have tried Norton (my default) & AVG. AVG even did a "boot-time" scan before Windows startup & found a Trojan called "HTML: Phishing-RM," but the issue still persists. The one thing I haven't tried is safe mode - didn't think to do that . I will try & let you know. Thanks
A bit off-topic, but pretty pathetic that after several decades, Microsoft operating systems still need virus scanners because they are inherently unsafe.
There are wireless trackball mouse? Anyway if that's the case, try No. 3 from my list: 3. If you still have those old ball-bearing mouse that literally has a ball inside the mouse that controls the coordinates, you can open the bottom up and take out that ball and clean it. Many times when that ball gets too much dust on it, it will affect movement. You can even wash the ball under water and dry it if you want. If it still doesn't work, then it's the coordinating sensor sticks inside that's busted. Any problems in Windows would not affect mouse because it uses too small part of the OS and/or the motherboard resources. Aside from driver issues, if a mouse doesn't work, it's 90% mechanical. Bottom Line: I would get a new mouse.
Virus scanners are needed regardless what OS you use nowadays. Has nothing to do with something being unsafe or not. Just like any house you buy, you need a lock.
So, I reboot in safe mode & could not replicate the problem (that took a load off my mind, phew!) Then, did a clean boot to isolate which software was causing a conflict with my mouse. Turns out it is my printer - a Brother MFC-J5620DW model. Last wk, I started getting an alert that the yellow ink is about to run out - somehow this was causing a conflict in the background. Swapped out the yellow cartridge for a new one & problem solved! I'll send an email to Brother customer support to give them a heads up about this. Thanks to everyone for brainstorming this with me. And, a mighty big thanks to Userque for suggesting the safe mode option