Why is it slowing down on me?

[havi]

I built a computer less than a year ago. I don't have the specs with me, since I'm not at my house, but I have an epox 9NPA+sli motherboard, an Antec 550watt power supply, a Geforce 6800 vid card, 2 gigs of ram, 3 7200 rpm hard drives (two of them are in raid0, the other for backup), and an Athlon 64 3500+ Clawhammer 2000MHz HT 939 processor.

My problems are all involving the declining speed of the computer.

FIrst problem that I have had since the computer was built:
At first, whenever I'd restart the computer, it'd be back up and running in about thirty seconds - plenty fast. But whenever I would shut the computer down for a day or so and try to boot it up, it would take closer to four or five minutes to boot up. I do not understand why this is...

Second problem just developed over the last week or so.
The computer has been lightning fast up until about a week ago when it steadily started declining in speed. It has been somewhat gradual, but bootup time has drastically slowed down, games run worse and worse, Microsoft Outlook used to take about 3 seconds to load up, now it takes about thirty seconds, same thing with other simple programs like windows media player. I have run spybot search and destroy and adaware frequently, constantly kept the harddrives defragged, always installing the most recent drivers for vid cards and such, and I use the nvidia firewall that came with the motherboard and also another virus protection program that was provided and is run and updated by my college. I have checked the number of processes running, and that has not changed. Any suggestions as to what this might be? Would reinstalling Windows be a recommended option?

Sorry for the long post

Thanks a lot

[Mesaeus]

First of all, check the System log for disk errors. Your hard drive may be failing and Windows XP will automatically slow down the disk speed after a (small) amount of disk read errors. This might explain why it's so slow. Any other errors or warnings may point to a developing problem so describe them here and we'll try to help you. If you do have disk errors, your first priority should be to backup your data ASAP.

Reinstalling Windows probably won't help, use it only as a last resort. As for the Nvidia firewall, I have an nforce 4 board and I stay away from the nvidia firewall, it has cost me too much problems in the past. I use the built in Windows XP firewall, which is sufficient for my needs since SP2.