Problem is, you can never know what you don't know. Let's say I told you you could use another keylogger to find a keylogger? Nothing's guaranteed once your system is compromised. Same is true of any malware. Once malware gets in, I don't care how many anti-malware utilities you use, how good they are, there's no guarantee except completely reinstalling. We just ASSUME if nothing’s detected, or if detected and removed, all is safe. But that’s just for practical reasons.
Short of starting over w/ a brand new OS installation, I would recommend scanning the hard drive from another system you fully trust (e.g., a laptop that’s always been under your control, or even a friend’s PC). Pull the hard drive from your PC, hook it up to the other PC (a SATA port on the motherboard or perhaps a SATA external port, or it might require an external enclosure), and scan it from there. Because your hard drive is now just data to the other (presumably) clean PC, nothing on that hard drive is ACTIVELY working to prevent you from seeing malware (keylogger, rootkit, etc.). It’s still not a foolproof solution since I don’t know how effective any given anti-malware tools you choose to use will be. You definitely want to use a malware product that detects files on the hard drive that are NOT in the directory (a common ploy of rootkits and keyloggers). But at least it’s a much more reliable analysis than running those same anti-malware utilities from your own system.
In the future, if you suspect someone could compromise your system, I would use TrueCrypt whole drive encryption and a strong password ( http/www.grc.com/password
). Some versions of Windows also support BitLocker, a similar built-in feature (I personally prefer TrueCrypt even if BitLocker is available). And keep your machine OFF when there’s even a chance someone could gain access w/o your knowledge. At that point, the only way your system could be compromised is w/ a hardware keylogger or similar device.