My Compaq desktop, which has served me well for six years or so, might be coming to its end.

When I power it up, the Compaq logo comes on, then it takes me to the screen where I can choose between regular and safe mode. If I choose regular mode, Windows XP seems to start, but then I hear a clicking noise, and the computer loses power, then restarts and the whole process begins again. If I choose safe mode, pretty much the same thing happens, though Windows doesn't even appear to initiate.

It seems like a hardware problem--the computer's been slowing down over the years, but I keep all virus-scan programs, spyware, registry mechanics, etc, up to date. Might be worth mentioning that it's hooked up with a surge-protector, and our power-supply is reliable and not prone to surges or dips.

Any thoughts? Hard-drive failure?
Thanks in advance!

but then I hear a clicking noise, and the computer loses power

It would be pretty safe to assume that your laptop needs a new power supply. You could try a reformat/reinstall of Windows, but I doubt it would do any good.

Laptops are harder to take apart and do repairs on then regular PCs, so unless you're absolutely sure you can do it, I would say it's best left up to a professional.