I don't know what the hell you were thinking updating the gpu bios when your system is unstable.
First off to try and remedy this you are going to need another PC or a working GPU either way you need a display to test your system memory with memtest86 and run it for at least 9 passes or until it crashes.
http://www.memtest86.com/ Instructions are available on the download page for installation.
Test each stick 1 at a time. If the first module you test fails, put it in a different slot and test again. We want to rule out the problem as it could be either the ram, or a faulty slot even a faulty channel all together.
And while your pulling stuff out of your system, remove the motherboard and make sure the stand off's are in their correct positions. And that you don't have an extra touching the motherboard where it should not be.
Now if it turns out the motherboard and ram are indeed fine we need to start considering if the PSU is faulty. And with that take it somewhere that it can be tested. That will need to be RMA'd before proceeding with a re-flash.
Now the fun part with your GPU. This could be hit or miss given the nature of the incident.
Get a second usb stick, you're going to do a blind flash with the dos version of NVflash.
Download from either of these 2 sites:
Download the latest bios for your GPU here: http://www.techpowerup.com/vgabios/
And be 100% sure you are getting the correct bios for your card.
You are also going to need HP boot tool and Win98 dos files:
HP Boot Tool: http://files.extremeoverclocking.com/file.php?f=197
Win98 Dos files: http://files.extremeoverclocking.com/file.php?f=196
Here are the instructions read them carefully.