In that case the problem is that the system files of windows are corrupt.
If your data is important to you than buy a Laptop Hard-drive USB Enclosure and use that to connect your laptop's hard drive to another computer using USB and copy your data
Or you can take the laptop to Bestbuy store and they can do this for you and copy your data on another hard drive or a DVD.
Then you need to perform system recovery. It can be done two ways as explained below.
1. Using the built in recovery partition available in few models of Acer.
Please try the following key combination immediately after starting the laptop (when you see the Acer logo)Alt
If it has the builtin recovery partition, this should start the recovery process.
If prompted for a password XXXXX the process, enter six zeros (default).
It should start the Acer eRecovery process.
There will be 4 options:
1. Restore system to factory default
2. Restore system from user backup
3. Restore system from cd/dvd
Select option 1. and your computer will goto factory settings.
2. If unavailable in your model then you have to use the Acer Recovery Disc that came with your computer.
If no Disc came with your computer you can order one by going at this link : LINK
If you are not located in US let me know your country's name.
Put the Recovery Disk into your drive and restart your computer. Restart computer and on startup screen it will mention a Key to enter setup. Press that key immediately to enter setup. Then you will find many tabs. Goto BOOT tab. Change the boot order to make the CD Drive as 1st device in Boot order list and do Save and Exit. Then restart computer making sure disc is already in CD Drive. This will load computer from recovery disc.
Feel free to ask any question or concern you may have. I will be glad to help you.