Doownloaded firefox 2 days ago, now its not working at all and wont open

Question

I downloaded Mozilla firefox 2 days ago for my brother on his computer. (Windows Vista) He was previously using internet explorer and google chrome. He had asked me to remove google chrome as he wanted basic gooogle instead. I uninstalled google chrome and then tried to install google when this didnt work I decided to try downloading Mozilla to see if this helped which all went well and his compuer worked beautifully for 2 days then suddenly today the computer seems to have dumped Mozilla and reverted to the problem and wont allow him to open his gmail account, also Mozilla seems to have just disappeared. He tried to download it again but it isnt downloading. Help!!!!

Answer 1

Do a malware check with some malware scanning programs on the Windows computer.<br />
Please scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.
*Malwarebytes' Anti-Malware:<br>http://www.malwarebytes.org/mbam.php
*SuperAntispyware:<br>http://www.superantispyware.com/
*Microsoft Safety Scanner:<br>http://www.microsoft.com/security/scanner/en-us/default.aspx
*Windows Defender: Home Page:<br>http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
*Spybot Search & Destroy:<br>http://www.safer-networking.org/en/index.html
*Kasperky Free Security Scan:<br>http://www.kaspersky.com/security-scan
You can also do a check for a rootkit infection with TDSSKiller.
*http://support.kaspersky.com/viruses/solutions?qid=208280684
See also:
*"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked
A possible cause is security software (firewall,anti-virus) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.
Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.
See:
*https://support.mozilla.org/kb/Server+not+found
*https://support.mozilla.org/kb/Firewalls
*http://kb.mozillazine.org/Browser_will_not_start_up