Angela, you can download a legit DVD image of the SAME Windows 7 version that you had installed (see the sticker on your Acer (also note the activation key, you'll need it). Get the Windows image from HERE
, just make sure to also get the correct 32 or 64 bit version.
Then boot from the DVD that you burn from the image or make a USB installer using HERE
. Then use your key to activate.
Of course, if there is a hardware issue like a dead HDD, you will need to replace that first.