Hardisk Problem

IF YOU HAVE NOT , TRY THAT FIRST --YOU WILL SEE A BLACK SCREEN WITH WHITE WRITING RUNNING THROUGH UNTIL IT EVENTUALLY STARTS IN SAFE MODE.

Once started (if that works) then click start, right click computer, click manage, then click Event Viewer, and look for exclamations , or, errors.

This will at least tell you what caused it. If it was an update -uninstall that update while in safe mode- driver updates, as well as windows updates can cause this problem.

Alternatively, you should get a choice on system restore, at the F8 start up= choose a date before this happened (your data is prettysafe, as Windows mainly goes back to the time at least before the fault.(page 142 in your manual)http://www.manualowl.com/m/Acer%20Computers/Aspire-5732Z/Manual/114476?search=recovery&x=87&y

I see this has Vista installed by the manual, if you do not get a restore point,you can use your Vista disk (if you have one) to repair the start up= this will be an option when you start from the Vista disc. (page 142 of your manual)

 If you have not got a system disk, then you can try the recovery partition

Press F2 on startup, then d2d recovery- then check that it is enabled- if it is not enabled click on the f5, or f6 button to enable it. press enter press esc, press f10 to save and exit

On restart hld down the alt button, and press f10 to boot into recovery from hard disk-or all origainal factory settings.

On here you will find options to just restore windows and leave data intact, or restore to factory for wholw of hard drive. Your choice, but if you value your data, it could be wise to connect your hard drive to another lapto/pc using a caddy, and save any valuable data. 

thttp://support.acer.com/acerpanam/notebook/0000/Acer/TravelMate4650/TravelMate4650faq5.shtmlo

It could also be a virus, and the easiest way then is to totally reinstall to factory, unless you want to download to another laptop/pc and burn a virus scanning disk from McFee, or, Avast, AVG. AND RUN A SCAN ON STARTUP, FROM THAT DISK

If your hard drive is getting faulty, this can give similar problems, and it would be useful if you had a operating system disc, and run  chkdsk /r   from a command prompt, in the repair mode, of the disk on startup.

I hope this a help to you-