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.