Can't Log in! Help Please!!


Hi all, I have a Macbook dual processor that originally came with Tiger, but now is running Snow Leopard. I think I may have a virus because after downloading a file off the internet, I can't log in anymore. Every time I type my password in (correctly) a blue screen pops up, and it immediately kicks me back to the login screen. It does the same thing when I try to log in in safe mode. If possible I'd like to keep all of my files and info, but if needed I can wipe it out. I no longer have the Snow Leopard CD, so if I do need to wipe my computer, I'd like to do everything possible to do it without deleting Snow Leopard and restoring it back to Tiger. I DO have the Snow Leopard start up disk for a Macbook Pro if that makes a difference. How can I fix this?? Please help!
You may need to reinstall OS X.
First, try to boot to the MBPro disk, although it probably won't let you reinstall OS X.
You _should_ be able to go to the Utilities menu when you are booted to that DVD, and run Disk Utility.
Select your hard drive, and click the Repair Disk button (different from Repair Disk Permissions.)
If the hard drive test OK, Quit Disk Utility, then go back to the Utilities menu, and choose Reset Password.
Choose your hard drive, and change the password.
Restart to your hard drive, which will boot to the login window, where you would enter your new password to log in.

This _might_ not help, so you may need to reinstall OS X (and the Snow Leopard OS X installer that you have, again, won't help you)
I suggest that you should have your own Snow Leopard installer DVD, which Apple still sells here:
And, it's less than $20 now.