Now I don't know if your system came with sp1 already installed and you were just trying to update to sp2

So in case your system did not have sp1 installed when purchased and was just Vista, here is sp1 first

vista sp1
Download Windows Vista Service Pack 1 - Vista SP1 (Full package)

If that is already installed or you are installing from above link, then here is SP2
Download Windows Vista Service Pack 2 - Vista SP2 (Full package)

Note: when downloading these from this wwebsite, go down till you see 'Click Here to Download", you may have to wait 10-15 secs for the download box to come up - wait for the download box to come up and don't click on this on next page:
If something goes wrong, try clicking here to download from Microsoft.com
-Wait for download box to come up

Now before vista will let you update to sp2, you must have 'ALL" updates previously to that point
-Meaning when ready to install sp2, you must use windows update and install 'Every' update avail

After all updates are installed, you are ready to install the SP2
-It will go through same process you have gone through before (but quicker as from hard drive)

With that said: It will go through same steps as far as restarting and go to steps 1-3 and it will take a long time (be patient) When I had an Acer, it took around 3 hrs or so (I almost gave up, but didn't and it worked)

Hope all this helps out

Thanks for your suggestion but I can't download anything as my computer only gives me two screens the "downloading SP 3of3 - 0% complete - do not switch your computer off" this screen last for about a minute or so then a blank black screen for over a minute with little green lights moving from left to right within a rectangle box then it goes back to the start - it won't let me do anything else - very annoying!!

The information I had given above is if you choose to do a full system recovery back to factory settings as when you first purchased it

If you choose to do the full recovery and are having a problem with doing that, should be able to help

Back a couple post ago, I mentioned worse case scenario - this would be it

-start from scratch as if new

Try to boot the computer up in save mode and restore it to a previos state if this doesent work. If this has no efect the boot up from the recocery disk and select ''repair your pc'' then click next when you see the system recovery options click on startup repair or If you wernt able to boot it up in save mode for the system restore you can go ahed and do that

I tried to boot the computer on safe mode but when I press the enter key nothing happens!

To get into safe mode, tap the F8 key when the computer is starting

How to open safe mode . Read the following link
Safe Mode in Windows XP