Avast is arguably the best "free" AV program out there with minimal nag screen intrusion (but not zero.) Norton is not only trash it's harmful. Get that crap away from any computer you care about.
NEVER, EVER use Combofix unless you (1) know what you're doing and (2) are desperate. It *can* fix some nasty problems but it can also trash your system's integrity and if it does the latter there's no coming back. It's a last-ditch attempt to save you from a reload. Malwarebytes is *much* safer.
Never, ever trust your data if it's only in one place. Devise, *test* (to make sure it works) and use a backup system of some sort. If you care about your information at all that system must include some sort of off-site storage on some sort of basis (e.g. rotating physical media, etc.) I've got data on my systems from the 1980s and I've yet to lose it despite having suffered multiple malfunctions over the years, and this is why. Either do this right or you *will* lose something you care about eventually.
An SSD is an excellent option and should be first on virtually anyone's list, but NEVER degrag them. They gain zero from doing it and it costs you material percentages of the drive's life. In addition TRIM has to be on, and it should be if you do the move to it properly (or a new install onto it.)
Be aware that "consumer" SSDs (that's most of them) are NOT power-protected. If you lose power unexpectedly, and that includes hitting the switch without shutting down first, they can be (read that as "usually will be") corrupted silently, *including* data that was not being written at the time. The reasons for this are a bit complex but have to do with the fact that to write a block that once held data you must read/erase/write, and the units in which this is done are MUCH bigger than what you usually want to write (typically 4MB or more.) This means that data that was not being written has to be read and then re-written, so "static, at-rest" data is ALWAYS at risk when a write is being done.
But.... the Intel 730 series SSDs, which are reasonably-priced, DO include power protection -- and I KNOW it works because I have software that can load-test it "in anger" and have verified that it in fact loses nothing on a cord-pull. IMHO they're worth the (small) extra scratch and the (small) loss in performance over the fastest SSDs for this reason. They are not only suitable for home purposes but also are suitable for light-duty applications in professional use (e.g. data centers and similar) for this reason -- and as such I won't buy anything lesser even for a personal, desktop machine. The 240Gb model is about $150 on Amazon, which is a very nice price for a fast and *safe* device. They also have a 480gb model for about $250.