Hi Dear, My Acer Laptop is used without anti virus for 1week after that computer

Start the computer, and right after the BIOS shows the checksum etc and the screen turns dark, press & hold the F8 Key. The Safe Mode options list will appaear... select the Safe Mode with Networking option, and go Online to do a Virus Scan, while the scan is running, download a free antivirus and when the online antivirus finishes the scan, restart or turn off the computer and disconnect the internet. Start the computer and install the Antivirus before going online again.

Online Antivirus Scanners HERE
Bitdefender or Hose Call are excellent options

Download Avast 6 Free Antivirus HERE
OR
Download AVG Anti-Virus Free Edition 2012 HERE