I'm not sure what's going on with your Windows 7 computer, but it's possible you just need to do a clean install of Windows after backing up your data and wiping the hard drive. If you consistently have problems with Windows, you might consider Linux or a Mac.
I have almost zero experience in the world of Macintosh, but I have used Linux for about a decade and have been running it exclusively for the last 4 years.
Linux is a very solid desktop operating system, but it is limited. If you use your computer for web surfing, instant messaging, office programs, and other typical functions, Linux is great. If you want to get into advanced multimedia editing, RAW photo workflows, or anything rather complicated, Linux is going to be a struggle. It's also not a good fit for gamers.
Personally, I run openSUSE with KDE4 and it's been great. I've also installed it on computers of family members who have had excessive virus trouble in Windows. Six months in they're all happy as their computers have been running quickly and without problems.
I think Linux is more secure than Windows for a couple of reasons. First, linux-based viruses don't really exist. Nobody writes them. Second, Linux is great at separating admin and user priveleges. Many distributions go so far as to install all root (admin) files on a separate hard drive or partition. This segregation of system files and isolation of the user environment prevents malicious files from hiding themselves deep in a system folder and running all sorts of evil commands. For whatever reason, Windows has just never done a very good job of handling permissions and guarding root access.
This is a good article about Linux security in comparison to Windows.
As a seasoned Linux user, I can tell you it's not for everyone. No matter what the Linux Cult tells you, there's a lot that the OS just doesn't do well. And no matter what you read online, there's really no way of knowing if it will work for you until you use it for a while and make a decision. There's a bit of a learning curve, but it can be a good fit for some users.