Ahh...it's looking a little more clear. YES! MacKeeper is a malware. That can explain a lot of your issues. As well, since you don't maintain your Mac, chances are you have other Malware installed in it. The flag was that "Download Now".
I too don't like change much, so I make sure that if I DON'T have to update, I won't. I've been a Mac user for 20+ years, and I've learned that some updates aren't always the best things to do. Especially if your system is running perfectly fine without them. Put it this way, I just upgraded from SL to ML. I don't usually update to the next OS from what I currently have, until the latest OS is in it's final stages, and the newest one is coming out. Eg. Mavericks is the latest OS (one ahead of mine), and Yosemite is slated to be released in a month or two. They day I upgrade to Mavericks is the day, they announce the next OS after Yosemite. My reasoning behind this, by the time I upgrade to a new (older) OS, it would have had most of the bugs and kinks ironed out of it.
But I digress. Having a clearer picture of your practices, I would suggest this. Back up all your important files. ie. documents, pics, family videos, etc... Reformat your HDD (use the system disk that came with your Mac, or create a bootable USB drive with the OS you want to install). Boot from either one of those, and format your drive to Mac Journal Extended. Reinstall OS and any other apps you use.
Then...be diligent in what you do. Stay away from MacKeeper, or anything that pops up on your browser asking you to install something. Macs may be pretty much immune to most virus out there. But it's not completely invulnerable. Especially against Malwares. Practice internet smarts. Don't open files from emails you don't know. If it's sent from a "friend", but seems oddly suspicious, contact the friend directly to find out if they had sent it to you. 9/10 times, they didn't. Which means they got compromised as well.
Here are couple of links in how to create a bootable USB drive from an OS install app (not update app), and steps in how to format and install. Mavericks is free to download from the App Store. As much as I love SL, and wish I could have stuck with it, it's inevitable that you will need to upgrade.
Creating a bootable USB flashdrive
How to create a bootable USB to install OS X - TechRepublic
Here's a much simpler way:
DiskMaker X
Formatting HDD
How to Format Your Mac's Hard Drive - Tuts+ Computer Skills Tutorial
Installing OS
This one actually includes info on the above topics as well:
How to Do a Clean Install of OS X Mavericks
Hope this helps. This is how I've learned to be my own repair guy on all my Mac systems. I've only ever gone in for repair once. And that was back in 1994. Since then, I taught myself how to troubleshoot and fix. Macs, in my experience, are so well built, it's rare that you will get any hardware issues. These you do need to get serviced, unless you know how to solder, and now electronics. lol Some hardware issues, is just a matter of replacing a HDD or graphics card. Or bad ram. Those are simple to do. But for the most part, any issues I've ever dealt with all software based. Simple troubleshooting and maintenance can minimize these issues, before they become bigger more annoying issues.
Good luck.