Cloning software is ideal for this. If you bought the drives from Seagate, download their Disk Wizard package from their website for free. It can make clone copies TO a Seagate drive from any source. If you bought from WD, their package is called Acronis True Image WD Edition. Each of these is a VERY good customized version of a 3rd party package, Acronis True Image. Make sure to get and read the manual, because these tools have lots of features you need to find and understand - cloning is only one of them. If you bought from some other maker, check their website for similar tools. They are usually used to help you migrate from an older drive to a new larger unit, and can make the clone so the new unit completely takes over as the C: drive you boot from.
Now here's an interesting possibility. You believe your MBR has been damaged. When you make the clone copy and it is made bootable (the normal default process), the clone MIGHT just have a fresh MBR and Partition Table created on it, rather than merely copying the possibly faulty old one. If that happens, just making the clone might solve your problem. So, once you have that clone onto the new HDD, remove the old HDD and mount the new one in its place and see if your machine just boots up OK.