Error 0x80040154

Hello technitions,
i need help fast, every time i try to update windows defender i get an error messege (above), this is the same when i try to update windows vista, McAfee security centre and also when i try to sign into Windows live messenger, this is what i have done:

1. installed CCleaner and did a CC scan plus a registary scan, didnt work.
2. Tried uninstalling messenger with command pormpt (administrator and safe mode), add or remove programs and also tried the Zap messenger but did not work.
3. Tried using McAfee security centre (scan)- failed
4. tried Restore system but that had an error to.

Basically, this is the problems i am having:
1. cant open any messeges on MSN hotmail (normal internet browser)
2. cant update ANYTHING to do with the system
3. Failed to uninstall messenger with every possible method
4. I keep getting McAfee icons appearing in the bottem left bar (were the clock is and messenger icon is) and everytime i scroll over to them they dissapear.

So all im left with is a broken Internet browser and a out-of-date computer, Please help, wiping my whole hard drive and re-installing vista (or windows 7) might be my only choice since i have run out of methods.

Yours sincerlary
Kearen

p.s: I am using Mozilla Firefox and currently using Windows vista home premium SP2, with a AMD athlon 7450 Dual-Core processor, Nvidia GeForce 8200. The computer i am using is a Acer Aspire x desktop PC. Also ive had these problems for the past 5 months. Please help me!!! :)

Have a good week ahead!!!