|Are you sure it is safemode, normally a window will appear, informing you that Windows is running in Safe Mode, and the words "Safe Mode" will appear on all four corners of the screen.|
If indeed the system only boot up in safemode, you should try a Clean Boot of your machine to help isolate the culprit.
0. From the safemode desktop, click Start, and click Run. The Run window appears.
1. In the Open box, type msconfig and then click OK. The System Configuration Utility appears.
2. From the General tab, click Selective Startup radio button.
3. Uncheck all options with the exception of "Load System Services" & "Use Original BOOT.INI".
When you are done the following should be in an unchecked state, *Process SYSTEM.INI File, Process WIN.INI File & Load startup items* or you've missed something.
4. Click Apply, and then click Close.
5. When prompted to restart the computer, click Yes.
Now if it boot up in normal mode you should get a message to the effect of the changes you just made in msconfig, don't worry about it, but make sure you put a check in the box that says "Do not show me this message again" and click the "OK" button.
If you get as far as above, post back to let us know.