500 internal server error

[Sycoloco1212]

anyone help me? i was just editing the header template, i have been working on it for days, and hours of me working on it, i tried saving it and got a 500 internal server error, now all my other 8 domains i try going to have 500 internal server error, and i asked them for support and this is what they said..

Hello,

Thank you for contacting Lunarpages support.

If your site has been compromised, then usually the virus will insert actual code onto your site through a vulnerable script, most likely via a form or script you have running that has not been updated to the most recent version. Generally, to resolve this issue, you will need to go through all of your scripts (usually in default or index files) and examine them thoroughly for any added code.

i have over probably 1million files on this database been using it for 3 years and no problems like this till now, i have no idea to start searching, the header file i have been editing is vb4....... i need help on this if anyone can help me thanks =P or any suggestions on what might be the problem..