People here are mixing up file sharing and computer backup.
Dropbox, One Drive, et. al. Are for sharing files, and keeping them synced between devices. By default, the files are backed up to the cloud. But it's a. a very limited system (small space allowances, only sync a specific folder), and b. Completely manual (whatever you want backed up has to be copied into the watched folder).
What OP wants is a backup system. Unlimited (or tremendously high) storage space, complete system backup, and constant monitoring and syncing (incremental backup). For these he'd need Crashplan, Carbonite, or something like that.