In order to troubleshoot the issue better, please provide more information.
Are you gettinng any error message at the time of booting the computer in Safe Mode?
Are you able to boot to the desktop in normal mode?
I would suggest you to perform Startup Repair and check if the issue is resolved.
Startup Repair is a Windows recovery tool that can fix certain system problems that might prevent Windows from starting. Startup Repair scans your computer for the problem and then tries to fix it so your computer can start correctly.
Startup Repair is one of the recovery tools in the System Recovery Options menu. This set of tools is located on your computer's hard disk and on the Windows installation disc.
1. Remove all floppy disks, CDs, and DVDs from your computer, and then restart your computer using the computer's power button.
2. Do one of the following:
3 Put the Windows 7 installation disc in the disc drive, and then start the computer.
4. Press a key when you are prompted. Select a language, a time, a currency, a keyboard or an input method, and then click Next.
5. Click Repair your computer.
6. Click the operating system that you want to repair, and then click Next.
7. In the System Recovery Options dialog box, click Command Prompt.
8. Type Bootrec.exe, and then press ENTER.
type the following commands at the Windows RE command prompt:
bcdedit /export C:\BCD_Backup
c:
cd boot
attrib bcd -s -h -r
ren c:\boot\bcd bcd.old
bootrec /RebuildBcd
/FixMbr
The /FixMbr option writes a Windows 7 or Windows Vista-compatible MBR to the system partition. This option does not overwrite the existing partition table. Use this option when you must resolve MBR corruption issues, or when you have to remove nonstandard code from the MBR.
/FixBoot
The /FixBoot option writes a new boot sector to the system partition by using a boot sector that is compatible with Windows Vista or Windows 7. Use this option if one of the following conditions is true:
The boot sector was replaced with a nonstandard Windows Vista or Windows 7 boot sector.
The boot sector is damaged.
An earlier Windows operating system was installed after Windows Vista or Windows 7 was installed. In this scenario, the computer starts by using Windows NT Loader (NTLDR) instead of Windows Boot Manager (Bootmgr.exe).
/ScanOs
The /ScanOs option scans all disks for installations that are compatible with Windows Vista or Windows 7. Additionally, this option displays the entries that are currently not in the BCD store. Use this option when there are Windows Vista or Windows 7 installations that the Boot Manager menu does not list.
/RebuildBcd
The /RebuildBcd option scans all disks for installations that are compatible with Windows Vista or Windows 7. Additionally, this option lets you select the installations that you want to add to the BCD store. Use this option when you must completely rebuild the BCD.
