My computer has for some reason stopped allowing me to install Windows updates. I can download them automatically like normal, but they all fail to install. For a while I was just downloading them each from Microsoft's website and installing them manually, but that was getting tedious. Any ideas on how to make Windows Update able to install them again?

Give us more information....Operating System, Anti-virus, Firewall, Hard drive size, how much RAM...etc.?

Widows XP Media Center 2005
150 GB Hard Drive (108 GB free)
1 GB RAM
3.4 GHz Processor
No anti-virus yet
Windows Firewall

The anti-virus is missing and I'm just using Windows firewall because I just did a system recovery last week. I had Norton before, but I really didn't like it so I'm probably getting something else sometime this week.

Hi what you should do ASAP is install an Anti-virus program.
If not you will have far more problems than not being able to update Widows.
Check.
http://forum.networktechs.com/showthread.php?t=50
There are Free ones available.

Go HERE (http://forum.networktechs.com/showthread.php?t=50)
download, install and update one of the free anti-virus programs PP notes here. All are good. Have used AVG and am now using Antivir. Like it really well.
Does the XP have SP1 or SP2 on it?

It has SP3.

http://support.microsoft.com/kb/943144