MPro, 10.7.5 mouse/keyboard intermittently become unresponsive

Question

I am running OS 10.7.5 on a 2009 Mac Pro and recently the mouse started to intermittently become unresponsive. I usually can fix this by conecting the mouse to a different usb port but last time it happened this didn't work and I also lost the keyboard. I switched both mouse and keyboard and problem persisted, even when moving to different usb ports.  After several hard reboots the mouse and keyboard came back and has been working since. I know the second mouse and keyboard are good and I am able to ptint from all the usb ports on the Mac Pro so I son't think it's a hardware problem. Could this be some kind of driver conflict? There are two canon usb printer drivers installed and two network printers )Lexmark and Brother). I have been running software update regularly. No other problems and I do regular disk maintenance (Diskwarrior). There are two SSDs and two hard drives installed, 32 GB ram. No problems with any hardware that I know of. Could a memory error? Thanks in advance for any ideas as to cause or insights into tracking it down appreciated.

Answer 1

Please read this whole message before doing anything.
This procedure is a test, not a solution. Don’t be disappointed when you find that nothing has changed after you complete it.
Step 1
The purpose of this step is to determine whether the problem is localized to your user account.
Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”
While logged in as Guest, you won’t have access to any of your personal files or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
Test while logged in as Guest. Same problem?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.
*Note: If you’ve activated “Find My Mac” or FileVault, then you can’t enable the Guest account. The “Guest User” login created by “Find My Mac” is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.
Step 2
The purpose of this step is to determine whether the problem is caused by third-party system modifications that load automatically at startup or login, by a peripheral device, by a font conflict, or by corruption of the file system or of certain system caches.
Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem. You must hold down the shift key twice: once when you boot, and again when you log in.
Note: If FileVault is enabled, or if a firmware password is set, or if the boot volume is a software RAID, you can’t do this. Ask for further instructions.
Safe mode is much slower to boot and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal boot may also be somewhat slow.
The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
Test while in safe mode. Same problem?
After testing, reboot as usual (i.e., not in safe mode) and verify that you still have the problem. Post the results of steps 1 and 2.