1) Your event log shows 3 kind of errors- Boot performance, shutdown performance and DWM.
2) For the particular error highlighted in the snip, the boot duration is 43 seconds which is quite OK. However there are more severe errors there (Critical and warning) in the same task category. So the system occasionally thinks boot times are long.
3) For the the boot issues, you need to sort the event viewer list by "task category", then go through all the events you see in the “Boot Performance” category. Look for “Warnings” and “Critical” errors. For each such event, double click on the event, a window will pop up, click on the "General tab" and read carefully what it says. It would say "This application took longer than usual to start up.....".
Once you've done this for all critical and warning errors in Boot performance category, you'll know what the problematic apps are. If this event only crops up once, you don’t need to go on Red Alert. However, if you see the same warning more than once, then this is definitely a call to action. You can decide whether you really need that particular app installed on your computer, whether you need it to run at startup, whether you need to update drivers etc.
4) You can repeat this exercise for task category "shutdown performance monitoring".
5) Theres also a freeware program called Soluto
which can trace boot times for you, you can try that too.
6) For the DWM errors, it may be a resource contention issue. Try turning off aero (either disable aero or switch to a classic theme), if that makes the errors go away it may have to do with the graphics driver or the video card or insufficient memory or maybe multiple monitors connected. Also, try turning off the screensaver and see if it helps.