Usually if your graphics card overheats you'll start getting artifacts on the screen or a complete crash accompanied with a Windows message saying that your card has recovered from an error or just a complete system halt altogether. As long as your card isn't overclocked, is dust free, the fan is working properly, and the air has a good flow to escape your system then your card shouldn't be overheating. You can monitor the temps with third party tools that are easily found if Googled. If it's an nVidia card use nVidia Inspector. If you're you're using Dawnguard, then you should probably be using the Dawnguard Unofficial Patch as well. Skyrim Unofficial patch should also be used, tho I think that's a part of STEP. Make sure any additional mods you use are compatible with Dawnguard and Hearthfire as well. If they're not, then those mods could cause issues in certain areas of the game. Also, use BOSS if you're not and make sure your load order is correct. Like Farlo suggested, if you're not having any issues with just the completed STEP (no additional mods installed), then uninstall or deactivate anything that is not a part of STEP. Then test the additional mods one-by-one to find the specific mod that may be causing any issues. I think just about everyone here uses additional mods that aren't in STEP. Personally, I use around ten additional mods (most against STEP like Lockpick Pro...don't judge me! ) but none conflict and cause any issues because I've done the testing. Yeah, there is always a message that my graphics card restarted after a crah or something....Is this very bad? Of course i use the Unofficial Dawnguard Patch, but it is included in the guide so i did´t mention it, mentioning dawnguard was a bit confusing, sorry.