You've actually got a couple of things going on. One is to download and install Sentinel. The other is to deal with a bad SD card, which happens from time to time.
To download Sentinel, see this page:
Uniden BCD436HP Scanner (You may need to go to this page if Sentinel version 1.07.05 isn't on the first
http://info.uniden.com/twiki/bin/view/UnidenMan4/BCDx36HPSentinel)
Installing Sentinel is beneficial because you can update the scanner's firmware - firmware updates are made when issues are discovered with a scanner. This doesn't happen often, but most folks agree that keeping your firmware up to date gives best results.
Also Sentinel allows you to update the master database. While the database is updated weekly, most folks only do updates every now and then. I'll do an update if things in my state change (which you can determine by visiting the RR database page) or just before I go on a trip somewhere.
Now on to your bad SD card situation:
Download and install SD Formatter -
https://www.sdcard.org/downloads/formatter_4/
If your computer has a card reader, it's best to put the new card in it and perform the following operations. (It can be done with the new card in the scanner, but it takes much longer.) Here are the steps:
Insert the card in the device. Use Windows Explorer to locate the new card and note the drive letter. (If you use the scanner, connect the scanner to the computer and choose "Mass Storage" mode. Then use Windows Explorer to locate the card as described above).
Launch SD formatter and have it format the new card. The card will be where you noted it from the step above. (Some may say you don't need to format the new card, but sometimes new cards have "helpful" utilities and all they do is take up room on the scanner's card).
After the card has been formatted, launch Sentinel. Go to Scanner>Clear User Data. A pop-up window appears. Check the "Display all drives" box. Highlight the drive for the SD card as you noted previously and click the OK button. (This process writes certain files to the SD card that are needed for the scanner to function. I suspect those are the files that are corrupted on your current card).
Next, in Sentinel click Update and go to Update Firmware. If your scanner doesn't have the latest firmware, it will be updated.
Next in Sentinel click Update and go to Update Master HPDB. This will download the current database to your computer.
Lastly, in Sentinel click Write to Scanner, then OK to copy the database from your computer to the scanner.
Your scanner should be back in operation after disconnecting it from your computer.
While this sounds complicated at first, it is no different than any other kind of software or new shoes for that matter. A little uncomfortable at first, but with a little experience, things become more comfortable.