Let's find out if it's a hardware error (maybe the drive doesn't even start to spin the disks, or it spins but can't read them?). Start the machine and go into the BIOS settings by pressing a key. (On the initial screen there must be some indication, which key you should press, ESC, Del, or some function button. You could tell me, what is the exact type of your laptop, so I can check out the product manual for the BIOS settings.) When in BIOS, check if the drive's presence is indicated somewhere. For example in boot order settings, under the drives category.
It's possible that the drive itself is fine, and maybe the area responsible for booting was overwritten by some software process. In this case, you'll need to boot on a Windows 7 installer DVD, select the Repair function, and do a "Startup Repair". http://windows.microsoft.com/en-US/windows7/products/fe...
Hope you created a set of backup DVD's, if the hdd is stuffed, then so are you, as it has the recovery partition and Acer will charge you about £40+ for a set of disks.
Now saying that, all is not lost, you could hook up a second hdd and use cloning software to copy the recovery partition.
But before you do that, if the hdd is seen in bios or bios startup screens, it could just be the boot sector has got corrupt, so just boot off a Win7 cd and us ethe repair option to correct this and see if it sorts things out.