How to reformat acer aspire one
Put a Windows XP disk (has to be the full version not an upgrade) into the CD drive and the computer will ask to "press any key to boot from CD". Press a key. Follow the prompts, It is important to delete the partition when asked. Then recreate it. Format the drive with NTFS file system. The setup will go on to reinstall windows automatically.
Now, the only challenge is to reload any software drivers for components Windows does not find automatically. This is a little tricky. Do google search of Acer drivers or go to www.drivers.com.
Also, remember all your software programs need to be re-installed. For example, your Microsoft Office (word, excel, etc). Any games, any virus protection, Quickbooks, etc. The printer software also needs to be re-installed. Hopefully you still have the original disk or if its a Hewlett Packard go to their website.