Spyware or Malware - Casual internet use can incur Spyware and/or Malware. Spyware and Malware can slow your computer down considerably. Click here for more information.

Hard Drive Failure / Corruption - Hard Drive failure can cause your computer to slow down considerably. Hard Drive failure will be accompanied by other symptoms like strange noises coming from your computer, data loss or corruption, or consistent messages before booting involving CHKDSK. Click here for more information.

Viruses, Trojans, or Worms - If you have contracted one of these three, you may experience any combination of a thousand other symptoms. Speeding up your computer will be the least of your issues. Click here for more information.

Bloatware - Production, or Off-The-Shelf, computers often come with software you never would have installed if left to your own devices, especially Dell and HP products. HP Printers also install huge chunks of unwanted software, particularly if you install "extended services." It's also a sad fact that most, almost all, programs believe themselves to be so important that they must start when Windows does.

Need Windows Startup Optimization - This ties in closely with #4. Windows Startup can be optimized so that only necessary components start with Windows. Not truly deserving of its own line-item, but it DID bear repeating.

File Fragmentation - Your computer may need to be defragmented. This is a function of Windows System Tools and can be done at any time when you don't need your computer for a while.

Not Enough Memory / Memory Failure - To a certain extent, RAM is responsible for the running speed of a computer. If your computer has insufficient RAM, your computer will slow down when applications are running, or sometimes even just when Windows opens up.