No problem. The 5400 and 7200 are speeds in rpm. Done this loads of times and even with SSD in size between 128Gb to 500Gb.
If you do not want to re-install the system you can clone the disk with a Linux (free for download). The procedure is here. There is a good chance your system will run again in the new disk if it was just a failed system file that stoped you laptop from booting up.
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