Just tell me that you don't have databases on the system drive. :)
Seriously, what they said. If your databases aren't in simple recovery, they must have transaction log backups or the log will grow until it eventually consumes the disk. (Which is why I said "not the system disk." One of my lesser colleagues once installed software, including SQL databases, on the system drive, and it ate Windows.)
Also, there's no guarantee that those .mdf, .ndf, and .ldf files will attach off your backup, especially if there's any kind of time difference between when they were backed up. (They might, but it's not supported, and they might not.)
So... what Thomas Stringer and vonPryz said. Back up through SQL. Run DBCC CHECKDB. (Reindex, even.) Back up the backup files with Acronis.