My Toshiba Sat Pro L650 (PSK1KA-04102T) seems to be slowly dying on me.

For a few months I would randomly get a blue screen stating an error had occured, and the laptop needed restarting.

Then I had a message stating the battery needed replacing (no big deal).

And recently I kept getting the message that my 'windows has detected a problem, hard disk failing, back up now' etc.

I ran chkdsk, and there didnt appear to be any issues.

So I ran the windows software and backed up 500gb on an external hard drive. I ran superAntispyware & Malwarebytes (one of which picked up a trojan).

I got quite annoyed with the message (windows detect a problem) popping up every 5 minutes, I clicked 'Do Not Show this Message Again'. I regret doing this, because now I am unsure if it is ok or not.

Saying that, after starting the laptop, it takes about 5-10mins to open windows live mail or even google chrome.

Can anyone answer the following:

1) How do I turn on the windows message to let me know about the hard disk failing?

2) Now that Ive backed everything up (I hope), can/should I format the hard drive? 

3) or should I just buy another hard drive?

Thanks