I can't get the computer to let me in it has the error message UNMOUNTABLE_BOOT_VOLUME ITS A SONY VAIO DIGITAL STUDIO PCV-RX660

It is normal that people remove hard drives or reformat (scrub clean) the hard drive on secondhand computers. Open up the case and look for a hard drive. Then you will either need to fit one and / or buy a copy of Windows XP (virus magnet) operating system from Sony for that model. It is an old Pentium 4, so the best course of action would be to take it to your local waste disposal centre for recycling!

Sony VAIO Digital Studio
? DVD and CD-RW Drive
? Intel Pentium 4, 1.8 Ghz
? Movie Editing and Video Email
? 10Base-T/100Base-TX Fast Ethernet and V.90 Modem
? i.LINK
(IEEE 1394) Interface and USB Connectors

Sony VAIO Digital Studio PCV-RX660 Specifications

You must firstly install an operating system, assuming there is a hard drive/ssd fitted.
If no hdd fit an hdd and then place an operating system on it.