Looks like there's a problem with the laptop detecting your Hard Disk Drive. It could be a that the connection between the Hard Drive and the motherboard is loose, or the Hard Drive itself is no good. Has the laptop been dropped recently?
How old is the laptop? When did you purchase the laptop from Walmart? If its less than a year you should still be covered by Acer's One Year Warranty.
Try the following. Power on your laptop, then when the image on the screen comes on at the bottom it should say what button to press to enter the BIOS (be quick because it comes and goes fast). Press that button and look in your BIOS to make sure that the Hard Drive is being detected by the BIOS.
If the BIOS does detect your Hard Drive, then you can use a boot able disc to check the Hard Drive's status.
Post your findings......Good Luck.