I have a desktop PC running on Vista Home Edition (32 bit). There are 4 users on it and the only one who ever cleans it up is me. I run Norton 360 but the machine is getting slower and slower on boot up, startup of applications, on IE and just about everything else. I'm fairly sure that I have a number of Trojans, spyware, and malware in the machine. My other 3 family members have this "habit" of clicking "yes" to everything that comes up. I also know that Norton 360 doesn't catch everything. I've edited my registry in the past and am pretty good at removing tough virus, Trojans, etc. So I am good at this, just not knowledgeable. I don't use this computer all that much but the complaints from my wife and kids are requiring me to take action. I clean out the cache, temp files, cookies, etc. and defrag on a very regular basis.
I don't want to download some spyware scanner only to find out I have to purchase their software to remove all the bad things it found on my computer. I suspect that half the things found are installed by the free scans that are supposed to help you.
Anyway, what would be the best path forward (i.e. step 1, step 2, step 3, etc.) to get the machine running like it does when you first install on operating system? I have a Dell OptiPlex 755 dual-quad processor with 4GB of RAM, plenty of hard free hard drive space 500+ GB. Though not an Intel "I" series it still should be very fast but it's not.
PS I have Malware Bytes Anti Malware (free download), that I have run before.