For some reason, i've lost Msn Messenger.

I think it happened last night when i tried to log off and my computer crashed instead.

Now, though i have the passport and the Hotmail addy, i don't seem to have the program, though i still have the program in my programs file (if that makes any sense).. it won't run, i can't get it to run and if i go to the MSN site and attempt to download it again, my system crashes.. it's happened a half dozen times.. the screen just freezes and i have to CONTROL+ALT+DELETE to get out of it.

Now, you know i'm not the brightest bulb around when it comes to computers, but does anyone have any advice??.. i'm at a total loss... if i've lost the program, why can't i re-install it??

Thanks in advance