Over time, your computer's performance will slow down. But that doesn't mean you need a new machine. Maybe you simply need to fix your clunker.

My friend, Ed, has a homebuilt machine. Seven years later, it's still fast and reliable. Over the years, he's replaced the DVD drive (twice) and the power supply. He added memory, too, which was cheap. He also reinstalled Windows once. I've got more about that below.

If you're handy, or willing to learn to fix your computer, good machines last for years. Repair shops usually aren't cost-effective. Replacing a hard drive that way could run $300 or more. That's approaching the cost of a new computer.

A computer could be slow because of its hardware, software or both. Say your computer used to be fast and then you added programs. Maybe you overwhelmed the RAM (random access memory). If you have Windows XP, 1 gigabyte of memory should handle everything. If necessary, add memory.

Still slow? Your microprocessor may be struggling. Theoretically, you could update the chip, but don't try. Put up with it, or buy a computer with horsepower.

Got Windows Vista? Raise your memory to 2GB if you have a 32-bit machine. Owners of 64-bit machines can go to 4GB. Actually, you can go a lot higher. That's the big advantage of 64-bit computers. But you're probably just wasting your money adding more than 4GB of memory.

(Don't know 32 and 64 from Adam's cat? To see which kind of computer you have, click Start, then Control Panel. In the left pane, be sure you're in Classic View. Double-click System. Under System, find "System type.")

The Vista video system needs 128 megabytes of dedicated video memory, minimum. If you think you need more, go to 256MB. That is, if you have a video card. They're easy to swap out. Stop at 256MB, unless you're a serious gamer. If the video system is built into the motherboard, forget it, you won't be able to upgrade the video memory.

There's one other thing. A full hard drive, or one nearly so, will perform poorly. At the least, you need a gigabyte of free space. Add a second hard drive, if necessary. Or kill programs you don't use.

Free space is easy to check. Click Start, then Computer in Vista or My Computer in XP. Right-click Local Disk C: and click Properties. Check the pie chart.

At www.komando.com/news, I've got tips on adding memory, and links to sellers, which post tutorials.

Now, let's discuss software. Over time, Windows gets clogged with goop. You can try Disk Cleanup. Temporary files and other trash are not the issue they once were, but clean them out, anyway. Click Start, then All Programs, Accessories, System Files, Disk Cleanup.

Follow the directions. For sure, dump temporary Internet files and temporary files. Most of the rest can go, too. But if you're not sure, don't delete. Most hard drives have more empty space than Montana.

Also, check for malware. That includes viruses, trojans, adware/spyware and worms. You can remove this stuff with security programs.

Or, if you can't, check my site for tips. Some malware really takes root. Try to find the name. Practically anything can be removed with enough patience.

You don't have to pay for security software. I have plenty on my site, all free. In this case, you get a lot more than you pay for.

Unfortunately, you may well have to reinstall Windows. Go to my site, www.komando.com/news for tips and links for Windows XP. Windows Vista is about the same.

Before you reinstall Windows, you'll need to format the hard drive. That wipes out everything, not just Windows. So copy the stuff you want to keep, to a thumb drive or external hard drive. You'll have to reinstall most of your applications from their discs.