how to repair my PC ? pls help

my PC do not works well,
compaq presario SR 5859 pc, 4 G ram, intel cpu
buy for 1 yr

i try trojan hunter to scan, no infected.
i try restore to earlier system point, much worse

cannot login admin account,
very slow.
cannot open most exe program, IE did not works.
cannot boot from DVD, so I cannot recover it from my window 7 dvd,

use system mechanic to repair and done, fixed all points but

no improve,

use eset antivirus scan, no infect
use compaq pctool to check, all hardware is OK,

how can I fix it ?
pls comment and help,

My first recommendation would be to reinstall windows. Do a clean install and format the partition windows will be installed to. Backup any documents, pictures etc you want to keep before hand. Be advised though they could be infected so I would scan them all before ever putting them back on my PC.
You say you can't boot from DVD. Did you go into the BIOS and change your boot order so it goes to your DVD drive first?

factory reset > recover do not works
BIOS change to DVD boot order > but never booted by window 7 install DVD

my question is I try everything I know and cannot recover my PC
seems like a virus attack, but no sign after scanning and rechecking

the problem is " press any key to boot from dvd " never come up,
the PC just boot & start the harddisk again

the DVD is a bootable DVD, it is a legal version, I paid for this

Did you install windows on this PC originally? Is this DVD a full version or an upgrade version? Check your Windows 7 DVD to be sure it isn't scratched or smudged.

Is is possible to formatted with the cd?Go and change the way the computer boots then press any key to boot from cd and there u go a fresh start please note that if u have only 1 hard drive evrithing will be lost.Please have the drivers of the computer ready to isntall them before formatting.