Combofix isnt really to be used like AVG or Spybot as a on demand scanner. My first stop would be to get a AV installed and updated. AVG or another. I use this or this on my Windows machines. Because I like the simply GUI. I dont get caught up in ratings or opinions.
If all is good on your end. some tips for you:

10 Tips for Prevention and Avoidance of Malware:

There is no reason why your computer can not stay malware free.

No software can think for you. Help yourself. In no special order:

1) It is essential to keep your operating system (Windows) browser (IE, FireFox, Chrome, Opera) and other software up to date to "patch" vulnerabilities that could be exploited. Visit Windows Update frequently or use the Windows auto-update feature. Staying updated is also essential for other web based applications like Java, Adobe Flash/Reader, iTunes etc. More and more third party applications are being targeted. Use the auto-update features available in most software. Not sure if you are using the latest version of software? Check their version status and get the updates here.

2) Know what you are installing to your computer. Alot of software can come bundled with unwanted add-ons, like adware, toolbars and malware. More and more legitimate software is installing useless toolbars if not unchecked first. Do not install any files from ads, popups or random links. Do not fall for fake warnings about virus and trojans being found on your computer and you are then prompted to install software to remedy this. See also the signs that you may have malware on your computer.

3) Install and keep updated: one antivirus and two or three anti-malware applications. If not updated they will soon be worthless. If either of these frequently find malware then its time to *review your computer habits*.

4) Refrain from clicking on links or attachments via E-Mail, IM, IRC, Chat Rooms, Blogs or Social Networking Sites, no matter how tempting or legitimate the message may seem. See also E-mail phishing Tricks.

5) Do not click on ads/pop ups or offers from websites requesting that you need to install software to your computer--*for any reason*. Use the Alt+F4 keys to close the window.

6) Don't click on offers to "scan" your computer. Install ActiveX Objects with care. Do you trust the website to install components?

7) Consider the use of limited (non-privileged) accounts for everyday use, rather than administrator accounts. Limited accounts can help prevent *malware from installing and lessen its potential impact.* This is exactly what user account control (UAC) in Windows Vista and Windows 7 attempts to address.

8) Install and understand the *limitations* of a software firewall.

9) A tool for automatically hardening and securing Internet Explorer 8.0. Requires site registration for downloading. Changes some of the default settings of IE 8.0, Read the FAQ's. Or see a slide show Here and do it yourself. How to harden FireFox. for safer surfing.

10) Warez, cracks etc are very popular for carrying malware payloads. If you look for these you will encounter malware. If you download/install files via p2p networks you will encounter malware. Can you really trust the source of the file?


More info/tips with pictures, links below

Happy Safe Surfing.