You also had some issues while using Windows too, if I recall correctly?
Maybe your machine has some issue that isn't OS-related. It might be time to buy a new computer. Fixing that one is of course possible, but if the system is old enough and you need to replace a component (mainboard, RAM, etc.) sometimes it makes sense to just replace the majority of it due to compatibility issues and/or the cost of buying used parts while attempting to fix it.
Consider that, anyway. You might be able to reuse some parts, but generally you can count on replacing the mainboard, CPU, RAM, power supply (and case). I'd also recommend using SSD nowadays, if you haven't been using them for years already.
I don't recall what your system is, but chances are you can buy new parts for a system that will be much more powerful and probably quieter, without having to spend much.
As for that standby issue: I forget what the deal was, but I noticed some people having that kind of issue with some distros and some hardware. It may even be related to the sort of install you did (hibernate or suspend) and whether you added a swap file or not. I never let my computer go into hibernate or suspend; it's either on, or it's off. It's a desktop and consumes low power when I'm not doing anything demanding, so it's not worth letting "sleep". If anything I turn the monitor off, which saves the most power when the system isn't in use and I'm away from the desk.