Gateway EL500C desktop. Runs XP. No idea what else is "on" it, have not been able to gain access, other than opening and looking.

Started with a whisking noise inside at start, and she inquired around, ended up buying and sticking in a new hard drive.
Novice mistakes were made, still it never came back to boot up.
Spent time with tele-tech at Gateway, and touched a lot of parts. Still no boot, and no video. They told her new video card. Part acquired, and now I received the machine to put in the part - and after reseating it twice, chk'g all board components, and doing the piece by piece barebones boot - still nothing, and getting 2 beeps, no video - checked and replaced memory, all worked in another unit.
Help ? Mobo has 3 indicator lights that must be green (as told by gateway_) and all are green. Attempted to contact gateway support, and got tired of extremely long "hold".

Nan