I'm encountering odd problems while trying to rebuild my Windows 7 desktop PC. Background: I purchased my desktop PC (a Dell Studio XPS 435 MT, with Radeon HD4670 and dual monitors) about three years ago. It came with Windows Vista. Soon after I received this PC, I formatted the system partition and then installed Windows 7 Ultimate. Windows 7 worked well; over time, however, as I installed and uninstalled many applications, it began to exhibit odd behavior. About a year ago, thin horizontal black lines occasionally began appearing randomly across both monitors -- apparently leftover artifacts from application windows. In addition, certain actions (e.g., the display of User Account Dialogs, locking of the desktop, unlocking the desktop) no longer occurred simultaneously on the two monitors; rather, the primary monitor would update, a couple of seconds would transpire, and then second monitor would update. I updated the video drivers (from Windows Update, but not from AMD's site), without improvement. I had installed various codecs. I figured that the video drivers, codecs, and conflicting applications were contributing to the problem. I began rebuilding this PC over the weekend. I formatted the system partition, installed Windows 7, and applied perhaps 200 items (required and optional) from Windows Update, en masse. Perhaps this was unwise; some of the updates seemed to conflict with one another, causing odd error messages and occasional lockups. I re-installed Windows 7 again -- this time, only installing critical updates. Even before proceeding to install optional updates, including updated video and monitor drivers, the thin horizontal black lines are appearing again! In addition, the problem where certain actions are not simultaneously appearing on the two monitors is present again. I'm reluctant to install all of my applications and to restore from backups until I know that the hardware is OK. Any ideas as to what the root cause might be? Could something with the video card -- perhaps RAM - be at fault?