itunes, help me please

[bananasquash]

recently i got the new ipod nano. i wanted to connect it to itunes but i had the old version so i had to download the new one and when i went to install it, i couldnt because my windows version had to be updated. after a looong time i managed to update my windows and i installed itunes. It installed itself and then when i opened the programe it started to go through all of my songs and old playlists and put them in this new version and everything corectly as it was. but then it froze just before it ened so i closed the programe and then opened it again. I managed to put my whole library on my ipod and everything was fine and i switched off the computer.
Later on i decided i wanted to download some songs and then put them onto itunes and then ipod etc. but itunes wouldnt open. The timer would apear for 2 seconds next to the cursor but then nothing happened.
I tried to access itunes from different ways but it wouldnt open the window nor did a little itunes icon appear in the right hand corner pane.
I clicked the itunes setup thing again (the thing to install it) and 2 options were offered: uninstall itunes or the repair any missing or damaged files or something alon gthose lines. i did the 2nd option and that installed itself and then i clicked onto itunes. again it wouldnt open. i repeated this a few times still doesnt work. i tried restarting the computer and i tried opening it on a different user but still the same problem. i have tried the apple website for help but it doesnt work. when i open task manager itunes doesnt appear under applications and unde4r processes none of the cpu is being used by it. can ANYONE PLEASE TELL ME WHAT TO DO?

[fo3nix]

Unplug iPod.

Goto add/remove programs, and remove iTunes and Quicktime.

Then restart computer.

Then goto apple's website and re-download iTunes.

Then install iTunes, and restart.

Then try opening it.

Then, once iTunes works fine, plug your iPod in.