Hello !
First off, questions about hard drives should be posted in the "Storage" section of Tom's Hardware forums. Also, you double-posted this thread.
If by "combine" you mean a RAID setup, then it can't be done without losing data : To configure a RAID array, all drives will be wiped in the process.
However, if you buy a second hard drive, you can simply add it to your PC and you won't lose any data.
Good luck,
al360ex