You probably have some malware or viruses on it - sometimes they block other programs so you can't clean the system.

I just reinstalled Glary on my system last week , there is a place to click during the install to stay with the free program but it is small and in the lower corner I think.

But that doesn't explain the errors you got.. If you try to install it again look for the small button to continue with the free program.

I'm curious what the errors were about, if you get them again write down what it says. That could be one of the main problems you are having.

If you have any very important info on the computer (banking, ins., medical- that sort of thing)- i would copy it to a USB flash drive or thumb drive and then delete it from the computer hard drive.

you might try these free scanner/remover from reputable & safe sites -
http://www.kaspersky.com/virusscanner
http://www.mcafee.com/us/downloads/f...e-stinger.aspx
http://housecall.trendmicro.com/

this one is a regular download and can stay on your computer for you to manually run every so often as needed.
http://www.malwarebytes.org/products/malwarebytes_free

Do you have a cd of the operating system - XP with the SP3 - if you ever need to wipe it all and start fresh?
If you have the serial # for the computer - I think you can still request /order a replacement cd from Microsoft or maybe even Dell if it was ever registered.

As long as it boots up and isn't making any oddball noises it will keep going til something actually gives out on it.
Might not be the fastest or the most powerful , but as long as it goes online ...

If you don't need Windows for any personal softawre- you might consider this-
the totally free Linux operating systems - usually they use less resources than the Microsoft OS - so it is easier for the computer to process things faster.
Many of Linux distros will have a live cd that you can run from the disk drive to see if you like it before installing.
If you know how to burn iso files , you can download and burn your own to try, or order a cd or usb - super cheap.
[Linux Mint 12 DVD $4.95
Ubuntu 11.10 $1.75
Fedora 16 DVD $4.95
openSUSE 12.1 DVD $4.95
Debian 6.0.3 DVD set $31.95
CentOS 6.2 DVD $4.95
PCLinuxOS 2011.6 $1.75
Mageia 1 DVD $1.75

USB Flash Drives
Linux Mint 12 4GB $21.95
Ubuntu 11.10 4GB $21.95]

http://distrowatch.com/dwres.php?resource=major

My favs now are Lubuntu , PCLinuxOS, Mepis

just thought I'd let you know about that option as XP is only supposed to be supported til 2014 or so. I'll be going 100% Linux on my old pcs then.