How can I recover Win 7 SP1 OS on my Aspire 5738 from a partition on HDD?

I have latest versions of Chrome and Firefox as browsers. I don't prefer Internet Explorer 'cauz it stops responding often because of some reason. After installing windows updates one day, I realized that above laptop has been infected by a malware the very next day. Since I have MS Security Essentials as Anti-virus etc. security software. I used MS Malware removal tool to get rid of that malware successfully.

Somehow, one day above OS was not working good. I tried to restore it but it wouldn't. I don't have Extra hard drive and new recovery DVDs from Acer were not loading anything. Someone suggested that OS can be recovered from a partition that is on HDD. I don't know how to do that. Please help if someone knows how to!