No, he means a ROM Update Utility - a windows program which will wipe and unroot your phone and load a completely fresh set of software. There's information about these in the rooting FAQ (see the "all about rooting" sticky post in this forum, which is the red link in my signature). If your software is completely fouled-up, which this sounds like, that's the simplest way of getting it working again.
If your phone is GSM you can find a lot of them
here (for CDMA change the model to Bravo_C, but it only has one of those). You need to identify the one that corresponds to your previous software version (and network branding, if appropriate), though many networks can use the Gingerbread one.
If you could get into your custom recovery (boot while holding "volume down" key down, highlight "recovery" and press power button) then you could flash a ROM, but if it's a red triangle with an exclamation mark you see then I think your custom recovery is gone (or did you used some real old-fashioned way of rooting and not have one in the first place?).
ROM Manager is best avoided on a Desire (there's a sticky thread about that as well), and wouldn't work unless you get boot into android in the first place (so not much help with this).