Restore factory settings to acer aspire L3600?

Question

I am having problems with my new computer (acer aspire L3600). It isn't performing as it did when it was first purchased. It is running vista and has just had broadband installed. About a month later, the hard drive light is continually flashing and the internet is running slowly, though the internet provider says that there is nothing wrong with it. No new programs have been installed recently. I was wondering how to restore factory settings so the computer is set up how it was when it was purchased.All files and programs are backed up ready.Also no installation disks came with the computer.PLEASE HELP!!