CNET to the Rescue forum: Two PCs using my account unknown to me.

I think I've been hijacked or my PC has been compromised. It's been acting strangely for the past month. I tried to download the new Zone Alarm Free Firewall (from various other sites as well) but each time the download is blocked with the word "canceled." I've set C-NET as a trusted site with my Firefox browser, I've listed it in "exceptions" under Windows firewall and am at a complete loss. Also my email will not close. I sign in to my Hot Mail acct. and check the email and attempt to sign out. The green navigation "go-back" arrow stays bright as opposed to being grayed out as normally. I click on "sign out" and get the "sign in" sign, however, the green back arrow remains lighted and I sign out again, get sign in, arrow lighted, etc. A yellow banner pop-up at top of screen notes that "Firefox has blocked another computer from redirecting me to another site." I can only gray out the "back arrow" by going to File and clicking on Close Window and then restarting Firefox. Hot Mail gave me, just once, yesterday, a pop-up asking me to re-enter my password as two computers were using my acct. at the same time. Any ideas? Your site is tops and thanks for any help you might suggest. Joe M. Hayes, Del Mar, CA
PC Info: Micro Soft Windows XP, Home Edition, Version 2002, Service Pack 3: Computer - AMD Athlon 64X2 Dual, Core Processor 4200+, 2.21 GHz, 922 MB RAM, Physical Address Extension.