First, MEP 2014 is now an old product and is certainly not guaranteed to run successfully under any recent build of Win 10.
Second, the error messages you see are quite specific!
In the first one, a video file cannot be located; assuming it is still on your hard drive, you need to click on "Folder" and navigate to the the folder where the file is located.
The second one refers to an .HDP file, which is NOT a video file, but a Magix "helper" file. If you can load the associated video file the missing .HDP will be recreated.
The third message shows that the file you are trying to open contains no data that MEP can use.
The fourth shows that you are attempting to open a video file whose format and aspect ratio is different to the settings you have created for your project. You can either "ignore" the message or adapt the project to fit the file
You get rid of these and solve the problem by following the advice above and resolving the errors that are listed by responding to the individual messages.
Assuming the file(s) mentioned in the first popup exist in their original location(s) the most likely cause of the popups is you Antivirus Folder/Ransomware/Real time scan feature is blocking access to that folder.
Try turning off the Antivirus Folder/Ransomware/Real time scan features and load the project - if it loads OK then you need to add an exception in your AV for the folders where these files are - which should be within your Documents folder in the Project folder setting in Movie Edit Pro.
The fourth image is telling you that the video you are importing is not the same resolution and/or framerate of the project settings - in this case you are importing a lower resolution SD video with different Aspect ratio (4:3) in to a FullHD 1920 x 1080 16:9 project.
Click Do not adjust if you are wanting a FullHD 1920 x 1080 16:9 video on export - however do be aware that upscaling video will reduce the visual quality, and the 4:3 aspect ratio video will be pillar boxed ie have black bars to the left and right unless you crop it to the 16:9 aspect ratio and make the cropped section full screen.
Clicking adjust will change the project settings to that video and if you already have 16:9 video on the timeline it will be letterboxed ie black bars top and bottom and you will get the same popup again, and this time it would be the 16:9 videos you crop to 4:3 aspect ratio if you want them full screen.
In either case cropping loses some portion of the image.
In addition to John EB's comment above, I suspect that the 2nd and 3rd are related to the first, which is showing that the MP4 file MEP is looking for has been moved (or deleted) (if John's scenario that the Antivirus is blocking access isn't in play).
You need to find the file for MEP: click on "Folder", then navigate to the folder that now contains the file, click it then OK and you should be right: MEP will remember the new file location for next time. You may have to repeat this process twice for each missing/moved file.
A tip when doing this: drag the popup down a bit and then you can see the exact filename you are looking for.
If you have more than one hard drive, I recommend you keep all your video files on a drive that isn't the Windows drive. If this makes it easier to keep track of your files/projects and doesn't load up your C drive. Backups are also easier as you are not drilling down into the folder hierarchy of the C drive.