When you say you restarted the 'BOX', was the database shutdown clean? Sometimes back, I tested trying to do copy the DBF files while the database was open, and tried doing a normal shutdown. It was taking a long time so I did shutdown abort. And when I tried to startup, I got the errors you pointed out.
So my guess is, When you restarted your 'BOX', some of your scripts might have been copying your DBF files and the database was still open. The shutdown may not be proper. Did you check your alert log file? Does it say more?
Yesterday due to some reason, the backup kicked off every hour.(Database is in NOARCHIVE LOG MODE)
Did u find out why the cold backup was kicked off what is the reason? I suspect that OS couldn't copy some of your datafiles.May be this is a I/O error.Recovery is little bit tricky since the database is in Noarchive mode.It is glad that u had a cold backup.Otherwise in this scenario u could have lost some of information while recovering from that datafile.