Eugene's observations

There are three common causes of performance degradation:

1. Hardware that does not keep up with the latest software. Defragmenting the disk drive is a useful component of the housekeeping procedures I advocate. Beyond that, adding RAM is often a relatively cheap fix.
2. Too many competing background tasks. If there are more than half a dozen icons in the system tray (notification area) on the task bar, consider if any can be prevented from running each time the computer starts. Autoruns may be helpful here.
3. Malware infection. Make sure your Internet Security suite is up to date and run a full virus scan. After that I suggest you run two of the free programs I suggest on my Housekeeping page.