Many windows 7 users face this issue. The input font size on web pages becomes very small. Although the webpages appears fine, but if you enter anything like user name, password or fill a form, input fonts become very small. The problem is common on all browsers.
Follow the below steps to solve the issue:
Check the problem on all browsers, IE, FireFox, Chrome, Opera
If its problem with any particular browser, just rest all settings of that browser.
This problem is mainly caused by use of any third party non-compatible theme.
Right click on your Windows7 desktop >> Personalize >> Theme
Select one of the Standard Themes that come with Windows7 like Aero or a Windows Classic Theme.
Also, uninstall any theme software if you are using like Windows Blinds or AlienGuise and restart windows 7.
If after using default theme also, problem is not solved, probably your windows 7 is missing Arial fonts. There are 11 Arial fonts installed on windows 7.
Download below zip file, unzip the fonts and paste the fonts in:
Control Panel >> Appearance and Personalization >> Fonts
Download Arial fonts for Windows 7
Your problem should be solved now. Please let me know if your problem is still not solved, or you know any other fix of the problem.