Thanks for the post back...it provided everything needed. First, before you read the rest of this post, back-up all of your data! The error you are receiving is part of an early-warning system from Dell. It has detected that there is something physically wrong with your hard drive, and that a crash is imminent. However, there is no way of predicting how long your hard drive will last...could be a few minutes to a few months, but it will crash, permanently. To be safe, back up all of your data, and then replace the drive immediately, as it is no longer reliable. (For the Dell statement, click here.) That accounts for the slow performance, error messages, and crashes.
You'll want to check out a utility included in Windows XP called ''Microsoft backup'' (usually located under system utilities from the start menu). It will backup all of the My Documents folders, cookies, favorites, and personal settings on the computer, as well as any other custom data you want saved. You can also elect to create a system restore disk containing all the data on your computer (especially helpful in this case).
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As far as all of your protection (spyware, firewall, AV), I have a few suggestions. MS Antispyware is popping up with those messages because it's still in the BETA stages (for about another month), and Microsoft has not realeased any patches for it, just definitions updates. For now, you'll just have to ignore it and hope it's corrected in the final version.
Since you mentioned Norton Antivirus may be a trial only, you should look into getting a permanent solution. While it does provide great prtection, it's a little pricy and also a resource hog. Thus, I recommend AVG's free AV program, available from free.grisoft.com/freeweb.php (sorry...links are blocked due to the word "free").
MS's Windows Firewall only blocks incomming attacks, not outgoing. This means that while it will try to prevent anything from entering your computer, it will not stop the virus/trojan from sending your info out over the web or opening a back door if it manages to get inside your system. In addition, it lacks many of the advanced features of other firewalls. Thus I suggest ZoneLab's free firewall, available here. While it lacks some of the features of the paid version, it is considerably better than the Windows Firewall. (You could also purchase their full suite for $40 in order to achieve ultimate protection.)
Hope this helps,
John