The USB on my computer doesn't work properly.
I have a printer, external HD, flash drive on it.
They all worked perfectly until yesterday, today, all of them are acting up.

The symptoms are the following.

I plug in the connector, the speakers bleep, then an icon in the bottom right starts flashing.
I click on it, it says that the device is not recognised.

About once every ten times, it recognises the device, but when I try to do something, the "device is not recognised" message comes up again.
I've tried booting into safe mode, and delete all USB references in the device manager, then rebooting as suggested in striker's thread, but nothing changes.

I've tried taking redoing  the system back to a point made a week ago(Computer isn't in English so I a m not sure what the correct term is) but nothing changes.

Just before the problems started, I disconnected an internal HD that I use for back up.
That's the only thing that I can think of that could have caused the trouble.
I reconnected the HD, but it didn't fix the problem.

Any advice would be much appreciated

ETA, OS is WinXP pro.
I have anti virus software and Spybot Search and Destroy, ran both and came up clean.

repair install of XP (different from the repair console)
boot to the xp cd, select install, then when it detects an existing install do a repair
this will reinstall all the system files without having to reinstall all your programs

Thanks for your advice, I am backing up everything now.
As soon as I finish , I will try what you suggested

one way to test to see if the ports are actually bad is:

download knoppix  use nero or roxio to burn this iso to a cd.    this is a live cd so it won't make any changes to your current OS.  

you will need bitorrent to download from this link.    

 buy or borrow a usb mouse.  and plug it into your usb ports. and see if you mouse works.  preferable get a mouse that has the red LED's so you can see if its getting voltage.  

if it works  you have a windows/software problem.  if they don't you most likely have bad USB ports

I can't believe I forgot to put this in too

before the repair install, just try reinstalling the usb controller from device manager.

must have been since I had just gone through a repair install after moving my brother's HD onto a new motherboard and the idea of doing it was fresh in my head