The horizontal lines mean that Premiere can not find your footage.
Right-click the clip, reveal in project, then relink the media to its
new location on the new drive.
Relink an offline clip
Actually, these diagonal lines indicate that the source footage is shorter than that indicated in the timeline.
This can typically happen if you have placed footage in the timeline and subsequeently cut it with an external editor, AE, for example and reimported the shorter material under the same name.
To lose the diagonal lines, drag the end of the timeline placeholder left (to trim) until they are have gone. .
The project was relocated from one system to another.
I doubt the OP edited the original project with gaps of "overextended media" in the timeline.
The file extension indicated on the clip is .mts (AVCHD), and is likely a segmented clip
that was only partially relinked when the project and media were moved to a different system.
But if you look closely, it's not the entire clip that has diagonal lines through it, only
the end section to varying degrees - hence my conclusion.
only the end section to varying degrees
That suggests that a segmented file was not entirely relinked.
When relocating a project from one system to another, it is important that
the entire .mts media folder structure and all of its contents be moved
intact to the new system (preferably with identical drive and folder names
so relinking all media is automatic and trouble free).