"windows could not search for updates, an error occurred while checking for new updates for your computer.
error(s)found, code 80040154 windows updates encountered an unknown error"
Lots of possibilities here, but my guess is that either (most likely) you have some malicious software infection on your PC, or (very possible) your anti-virus package is messing things up, or (equally possible) Windows itself has managed to get in a muddle.
But before anything else. it's probably time to think about the state of your backups. If you can, back up what you think you need from your PC.
Both viruses and anti-virus packages are renowned for causing this kind of problem so it might be worth uninstalling any and all of those that you have TEMPORARILY and perhaps trying a different one to see if that sheds any light. Here are some suggestions:
http://www.5starsupport.com/ipboard/index.php?showtopic=30672
I found that by searching for "error(s)found, code 80040154" using my favourite search engine. Try it yourself, there will be quite a few hits.
You could try using the Windows repair functions. You might have a disc already which you can use but most often thesedays with cut-throat price competition you don't get one. You can make one easily enough, see for example
http://www.howtogeek.com/howto/wind...ndows-vista-repair-disk-if-you-dont-have-one/
When you've made the disc, boot from it and choose the repair option. It might work and it might not. If it doesn't we could be getting into deeper water. Time to ask how much it's worth to you not to have to format the drive and reinstall Windows from scratch. There might still be a simple way to fix it but it might be time-consuming to find it.
Lots more we can do, but see how you get on with that then post back here to tell us what happened.
There are forums all over the place where people are much better placed to help you than BCUK.