Hi Rania,

Since it can be due to various reasons, you can follow the below steps to resolve this issue:

1. Checking the system configuration:
Windows 7 uses lot of resources and space. It needs a minimum 1.5 GB DDR2 on 32-bit and 2 GB DDR2 on 64 bit versions, and it also requires a minimum of 15 GB on 32 bit and 20 GB on a 64-bit system. If Windows 7 is installed on a system with a configuration much lower than specified, it is bound to become slow.
So, first thing, make sure that your computer hardware meets minimum system requirements.

2. Checking Software and Hardware :
If you have installed any program or hardware after which your PC started to freeze, remove this hardware or software. If you do not remember the name of the problematic software but remember the date when the system was working fine then you can use the System Restore tool to revert system settings to a date when the system was working fine.

3. Check for Virus and Malware :
Sometimes the system may be affected by a virus or malware. Updating the Anti-virus and running a complete system scan is the best way to deal with it.

4. Multiple Programs eating memory :
It is also a good idea to stop all third party software and look for the error. To achieve this:

1. Click Start and type msconfig and press Enter.
2. Under the General tab, select Selective Startup.
3. Clear Load Startup Items and then select the Services tab.
4. Check the option Hide all Microsoft services and then select Disable All.

If the system starts working fine, you can enable one program at a time to determine which program is causing the problem.

5. Give the computer some time.
Give the computer a few minutes to process. Sometimes a computer may appear to be froze, but it is really just slow or busy processing a complex task.

See if the computer can respond to anything by pressing the Caps Lock key on the keyboard and watching the Caps Lock LED to see if it turns on and off. If the computer can turn on and off Caps Lock, then press the keys Ctrl + Alt + Del to open the Windows Task Manager.

If the Task Manager can open, highlight the program that is not responding and choose End Task, which should unfreeze the computer.

I hope this helps.

Regards,
Lokesh