I followed all the instructions for installing 24.04.2 64bit.
After installation, removing the install media, I can't seem to get the PC to offer the alternative boot to Linux. I've tried changing some BIOS settings with no luck.
I recreated an installation media, but now the machine doesn't even recognize that.
I'm at a loss as to what to do next. Does anyone have any ideas?
Can you tell more about your system? From Dell i have run into similar issues with dual boot before where there UFEI settings block bootloader from going into ubuntu.
Check this answer if that is helpful kubuntu/Ubuntu 18.04 ubi-partman failed with exit code 141. Does not detect my drive
As for your drive, you need to change the boot order and then you should be able to boot into your USB (as long as your USB is flashed correctly)
I was able to recover access to BIOS. For my motherboard it was as simple as unplugging the pc and allowing CMOS to dissipate. Some motherboards have a battery for CMOS that needs to be removed for about 30 secs. Subsequent to that I was able to re-install Ubuntu, using the advanced option to choose a disk, erase it and install Ubuntu there. (Convenient for me, since I have plenty of disks, but it remains that there are issues with installing Ubuntu alongside Windows 10 and setting up a dual boot option. I was unable to get that to work) I set up BIOS to boot to Ubuntu boot disk first, Windows Boot Manager second. This gives me a screen where I can select the disk with the Windows Boot Manager, or various boot options for Ubuntu. So far everything working well.