Why does my acer asprie 5742 keep clearing my cache?

This is a 7 year old laptop, and probably needs its internal CMOS battery replaced. Take it to repair location for verification and cost, since this requires disassembly.

METHOD 1: Reset Corrupt Thumbnail Cache Folder
First of all try to reset thumbnail cache folder so that it starts storing thumbnail cache files from scratch.
1. Press Win+R keys together to launch RUN dialog box, then type following string in RUN box and press Enter:
C:\Users\Username\AppData\Local\Microsoft\Windows\Explorer
Replace Username with your correct Windows user account name.
If the above trick doesn't work for you. Type appdata in RUN dialog box and press Enter. It'll open AppData folder. Now go to "Local\Microsoft\Windows\Explorer" folder.
2. Once you open Explorer folder, select all files/folders present inside it and delete them.
Some files might remain in the folder. Leave them and restart your computer. Now Windows should create thumbnail cache without any problem and it'll not delete them again.