Are you saying someone has "Unauthorised" use of your computer?
Browser history settings can be changed from within the browser's Tools > Options settings, but if the setting is set to delete all browser history when the browser closes, then the answer is no, you cannot get that back.
But if this is GMail accessed via a web browser, does your GMail account show any "Sent" mail folder? If you access your GMail by using software, eg Windows Live Mail, Thunderbird, Outlook etc, are there any "Sent" mail items showing in the Sent mail folder?
As to security, if you believe someone is hacking into either your Windows profile or your GMail account, these simple steps should help;
1] Windows - Make sure your Windows Profile, (Account), is password protected. Use a STRONG password, not a weak one.
2] Windows - Make sure all Admin capable accounts are password protected. Ensure the hidden System Administrator account is also password protected. DO NOT FORGET THESE PASSWORDS.
3] Windows - Never leave the computer when it is turned on. Always shut down when not in use.
4] Email - Do not allow the username and password for your email account to be 'saved' either by email software or browser. Always "Log in" with your email account username and password.
5] If you believe your email account has been hacked, CHANGE THE PASSWORD immediately, and use a STRONG password.
If this is a PC or laptop, remember, this is a personal computer, so if others have access, then it is up to you to protect your account.
It appears the browser history for today has been somewhat deleted and I can only see sites I have been to since I got home from work. I need to know if someone was sending gmail from my computer @ 10:48am. Is there another way to tell? Running windows 7