When TiVo is stuck on the "Welcome, powering up" screen it generally means that the motherboard cannot communicate with the hard drive. That generally means that the hard drive has failed.
If your TiVo is within the one-year parts warranty TiVo will usually replace it for $49. If not, the charge is $149 (although some have coerced them into only charging $49 if it's close to the expiration date and/or they threaten to cancel their subscription...YMMV).
If your TiVo is still under warranty and you open it, that will void the warranty. That said, the only way TiVo would know if you opened the box is if you tell them or leave behind some sort of evidence. You could pull the drive and run a diagnostic program such as WD's Lifeguard
. If the drive is faulty you'll need to either replace it or have TiVo replace your unit (but don't mention pulling the drive of course).
Many folks finding themselves in your position often opt to upgrade the TiVo HD's somewhat miniscule internal hard drive. You can purchase a pre-imaged drive from a reputable company like DVR Upgrade
or you can DIY. The link Roy posted above is for the Drive Expansion and Drive Upgrade FAQ
sticky thread. It has everything you need to know about upgrading your TiVo including recommended hard drives and Section V covers internal upgrades. The process is very simple if you're comfortable connecting a hard drive to a computer. Basically it means buying a bare hard drive (the 1TB WD10EVCS is recommended), connecting it to a computer and placing a TiVo image on it. If your drive were operational you could copy the image to the new drive using winMFS. It doesn't sound like it is so you'll probably need to also buy a clean image from DVRUpgrade called Instant Cake
. It's an easy process and well worth the time and effort. If you install a 1TB drive you'll end up with 157 hours of HD recording time!
Best of luck and let us know how it goes.